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POSTCONF(5)                   File Formats Manual                  POSTCONF(5)

NAME
       postconf - Postfix configuration parameters

SYNOPSIS
       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION
       The  Postfix  main.cf configuration file specifies parameters that con-
       trol the operation of the Postfix mail system. Typically the file  con-
       tains  only  a small subset of all parameters; parameters not specified
       are left at their default values.

       The general format of the main.cf file is as follows:

       o      Each logical line has the form "parameter = value".   Whitespace
              around the "=" is ignored, as is whitespace at the end of a log-
              ical line.

       o      Empty lines and whitespace-only lines are ignored, as are  lines
              whose first non-whitespace character is a `#'.

       o      A  logical  line  starts  with  non-whitespace text. A line that
              starts with whitespace continues a logical line.

       o      A parameter value may refer to other parameters.

              o      The expressions "$name" and "${name}" are recursively re-
                     placed with the value of the named parameter. The parame-
                     ter name must contain only characters from the set [a-zA-
                     Z0-9_]. An undefined parameter value is replaced with the
                     empty value.

              o      The expressions "${name?value}" and "${name?{value}}" are
                     replaced  with "value" when "$name" is non-empty. The pa-
                     rameter name must contain only characters  from  the  set
                     [a-zA-Z0-9_]. These forms are supported with Postfix ver-
                     sions >= 2.2 and >= 3.0, respectively.

              o      The expressions "${name:value}" and "${name:{value}}" are
                     replaced  with "value" when "$name" is empty. The parame-
                     ter name must contain only characters from the set [a-zA-
                     Z0-9_].  These  forms are supported with Postfix versions
                     >= 2.2 and >= 3.0, respectively.

              o      The expression  "${name?{value1}:{value2}}"  is  replaced
                     with   "value1"  when  "$name"  is  non-empty,  and  with
                     "value2" when "$name" is empty.  The "{}" is required for
                     "value1",  optional for "value2". The parameter name must
                     contain only characters from the set [a-zA-Z0-9_].   This
                     form is supported with Postfix versions >= 3.0.

              o      The  first  item  inside "${...}" may be a relational ex-
                     pression of the form: "{value3} == {value4}". Besides the
                     "=="  (equality) operator Postfix supports "!=" (inequal-
                     ity), "<", "<=", ">=", and ">". The comparison is numeri-
                     cal when both operands are all digits, otherwise the com-
                     parison is lexicographical.  These  forms  are  supported
                     with Postfix versions >= 3.0.

              o      Each  "value" is subject to recursive named parameter and
                     relational expression evaluation, except where noted.

              o      Whitespace before or after each "{value}" is ignored.

              o      Specify "$$" to produce a single "$" character.

              o      The legacy form "$(...)" is equivalent to  the  preferred
                     form "${...}".

       o      When the same parameter is defined multiple times, only the last
              instance is remembered.

       o      Otherwise, the order of main.cf parameter definitions  does  not
              matter.

       The remainder of this document is a description of all Postfix configu-
       ration parameters. Default values are shown after the parameter name in
       parentheses, and can be looked up with the "postconf -d" command.

       Note:  this  is not an invitation to make changes to Postfix configura-
       tion parameters. Unnecessary changes can impair the  operation  of  the
       mail system.

2bounce_notice_recipient (default: postmaster)
       The  recipient  of  undeliverable  mail  that cannot be returned to the
       sender.  This feature is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)
       The numerical Postfix SMTP server response code for  an  access(5)  map
       "defer" action, including "defer_if_permit" or "defer_if_reject". Prior
       to Postfix 2.6, the response is hard-coded as "450".

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)
       The  numerical  Postfix  SMTP server response code for an access(5) map
       "reject" action.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

address_verify_cache_cleanup_interval (default: 12h)
       The  amount  of  time  between  verify(8) address verification database
       cleanup runs. This feature requires  that  the  database  supports  the
       "delete"  and "sequence" operators.  Specify a zero interval to disable
       database cleanup.

       After each database cleanup run, the verify(8) daemon logs  the  number
       of  entries  that were retained and dropped. A cleanup run is logged as
       "partial" when the daemon  terminates  early  after  "postfix  reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)
       Overrides the default_transport parameter setting for address verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
       Overrides the local_transport parameter setting for  address  verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)
       Lookup  table  for persistent address verification status storage.  The
       table is maintained by the verify(8) service, and is opened before  the
       process releases privileges.

       The  lookup  table  is  persistent  by default (Postfix 2.7 and later).
       Specify an empty table name to keep the information in volatile  memory
       which is lost after "postfix reload" or "postfix stop". This is the de-
       fault with Postfix version 2.6 and earlier.

       Specify a location in a file system that will not fill up. If the data-
       base  becomes  corrupted,  the world comes to an end. To recover delete
       (NOT: truncate) the file and do "postfix reload".

       Postfix daemon processes do not use root privileges when  opening  this
       file  (Postfix 2.5 and later).  The file must therefore be stored under
       a Postfix-owned directory such as the data_directory.  As  a  migration
       aid, an attempt to open the file under a non-Postfix directory is redi-
       rected to the Postfix-owned data_directory, and a warning is logged.

       Examples:

       address_verify_map = hash:/var/lib/postfix/verify
       address_verify_map = btree:/var/lib/postfix/verify

       This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
       Enable caching of failed address verification probe results.  When this
       feature  is  enabled, the cache may pollute quickly with garbage.  When
       this feature is disabled, Postfix will generate an  address  probe  for
       every lookup.

       This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
       The  time after which a failed probe expires from the address verifica-
       tion cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
       The time after which a failed address verification probe  needs  to  be
       refreshed.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_pending_request_limit (default: see postconf -d output)
       A  safety  limit that prevents address verification requests from over-
       whelming the Postfix queue. By default, the number of pending  requests
       is  limited  to  1/4 of the active queue maximum size (qmgr_message_ac-
       tive_limit). The queue manager enforces the limit  by  tempfailing  re-
       quests  that  exceed the limit. This affects only unknown addresses and
       inactive addresses that have expired, because the verify(8) daemon  au-
       tomatically refreshes an active address before it expires.

       This feature is available in Postfix 3.1 and later.

address_verify_poll_count (default: normal: 3, overload: 1)
       How  many times to query the verify(8) service for the completion of an
       address verification request in progress.

       By default, the Postfix SMTP server polls the verify(8) service  up  to
       three  times  under  non-overload  conditions, and only once when under
       overload.  With Postfix version 2.5 and earlier, the SMTP server always
       polls the verify(8) service up to three times by default.

       Specify 1 to implement a crude form of greylisting, that is, always de-
       fer the first delivery request for a new address.

       Examples:

       # Postfix <= 2.6 default
       address_verify_poll_count = 3
       # Poor man's greylisting
       address_verify_poll_count = 1

       This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
       The delay between queries for the completion of an address verification
       request in progress.

       The default polling delay is 3 seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
       The  time after which a successful probe expires from the address veri-
       fication cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
       The time after which a successful address verification probe  needs  to
       be  refreshed.  The address verification status is not updated when the
       probe fails (optimistic caching).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
       Overrides the relay_transport parameter setting for  address  verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
       Overrides  the  relayhost  parameter  setting  for address verification
       probes. This information can be overruled with the transport(5) table.

       This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)
       The sender address to use in  address  verification  probes;  prior  to
       Postfix  2.5  the  default was "postmaster". To avoid problems with ad-
       dress probes that are sent in response to address probes,  the  Postfix
       SMTP  server  excludes  the  probe sender address from all SMTPD access
       blocks.

       Specify an empty value (address_verify_sender =) or <> if you  want  to
       use  the  null  sender address. Beware, some sites reject mail from <>,
       even though RFCs require that such addresses be accepted.

       Examples:

       address_verify_sender = <>
       address_verify_sender = postmaster@my.domain

       This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps  (default:  $sender_de-
       pendent_default_transport_maps)
       Overrides the sender_dependent_default_transport_maps parameter setting
       for address verification probes.

       This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps (default: $sender_dependent_re-
       layhost_maps)
       Overrides the sender_dependent_relayhost_maps parameter setting for ad-
       dress verification probes.

       This feature is available in Postfix 2.3 and later.

address_verify_sender_ttl (default: 0s)
       The time between changes in the time-dependent portion of address veri-
       fication probe sender addresses. The time-dependent portion is appended
       to the  localpart  of  the  address  specified  with  the  address_ver-
       ify_sender parameter. This feature is ignored when the probe sender ad-
       dresses is the null sender, i.e.  the  address_verify_sender  value  is
       empty or <>.

       Historically,  the probe sender address was fixed. This has caused such
       addresses to end up on spammer  mailing  lists,  and  has  resulted  in
       wasted network and processing resources.

       To  enable  time-dependent  probe  sender addresses, specify a non-zero
       time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time unit).  Specify a value of at least several hours,
       to avoid problems with senders that use greylisting.   Avoid  nice  TTL
       values,  to  make the result less predictable.  Time units are: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.9 and later.

address_verify_service_name (default: verify)
       The name of the verify(8) address verification  service.  This  service
       maintains  the  status  of sender and/or recipient address verification
       probes, and generates probes on request by other Postfix processes.

address_verify_transport_maps (default: $transport_maps)
       Overrides the transport_maps parameter setting for address verification
       probes.

       This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
       Overrides the virtual_transport parameter setting for address verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
       The alias  databases  for  local(8)  delivery  that  are  updated  with
       "newaliases" or with "sendmail -bi".

       This  is  a separate configuration parameter because not all the tables
       specified with $alias_maps have to be local files.

       Examples:

       alias_database = hash:/etc/aliases
       alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
       The alias databases that are used for local(8) delivery. See aliases(5)
       for  syntax  details.   Specify zero or more "type:name" lookup tables,
       separated by whitespace or comma. Tables will be searched in the speci-
       fied order until a match is found.  Note: these lookups are recursive.

       The default list is system dependent.  On systems with NIS, the default
       is to search the local alias database, then the NIS alias database.

       If you change the alias  database,  run  "postalias  /etc/aliases"  (or
       wherever  your  system  stores  the  mail  alias  file),  or simply run
       "newaliases" to build the necessary DBM or DB file.

       The local(8) delivery agent disallows regular  expression  substitution
       of $1 etc. in alias_maps, because that would open a security hole.

       The  local(8)  delivery  agent will silently ignore requests to use the
       proxymap(8) server within alias_maps. Instead it will  open  the  table
       directly.  Before Postfix version 2.2, the local(8) delivery agent will
       terminate with a fatal error.

       Examples:

       alias_maps = hash:/etc/aliases, nis:mail.aliases
       alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
       Restrict local(8) mail delivery to external commands.  The  default  is
       to  disallow delivery to "|command" in :include:  files (see aliases(5)
       for the text that defines this terminology).

       Specify zero or more of: alias, forward or include, in order  to  allow
       commands  in aliases(5), .forward files or in :include:  files, respec-
       tively.

       Example:

       allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
       Restrict local(8) mail delivery to external files. The  default  is  to
       disallow  "/file/name" destinations in :include:  files (see aliases(5)
       for the text that defines this terminology).

       Specify zero or more of: alias, forward or include, in order  to  allow
       "/file/name"  destinations  in  aliases(5),  .forward files and in :in-
       clude:  files, respectively.

       Example:

       allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
       Allow a sender or recipient address to have `-' as the first character.
       By  default, this is not allowed, to avoid accidents with software that
       passes email addresses via the command line. Such software would not be
       able  to  distinguish a malicious address from a bona fide command-line
       option. Although this can be prevented by inserting a "--" option  ter-
       minator  into  the  command  line, this is difficult to enforce consis-
       tently and globally.

       As of Postfix version 2.5, this feature is implemented  by  trivial-re-
       write(8).   With  earlier  versions  this  feature  was  implemented by
       qmgr(8) and was limited to recipient addresses only.

allow_percent_hack (default: yes)
       Enable the rewriting of the form "user%domain" to "user@domain".   This
       is enabled by default.

       Note:  as of Postfix version 2.2, message header address rewriting hap-
       pens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches  $lo-
              cal_header_rewrite_clients,

       o      The   message   is  received  from  the  network,  and  the  re-
              mote_header_rewrite_domain  parameter  specifies   a   non-empty
              value.

       To   get   the  behavior  before  Postfix  version  2.2,  specify  "lo-
       cal_header_rewrite_clients = static:all".

       Example:

       allow_percent_hack = no

allow_untrusted_routing (default: no)
       Forward mail with sender-specified  routing  (user[@%!]remote[@%!]site)
       from untrusted clients to destinations matching $relay_domains.

       By default, this feature is turned off.  This closes a nasty open relay
       loophole where a backup MX host can be  tricked  into  forwarding  junk
       mail to a primary MX host which then spams it out to the world.

       This  parameter also controls if non-local addresses with sender-speci-
       fied routing can match Postfix access  tables.  By  default,  such  ad-
       dresses  cannot match Postfix access tables, because the address is am-
       biguous.

alternate_config_directories (default: empty)
       A list of non-default Postfix configuration  directories  that  may  be
       specified  with  "-c config_directory" on the command line (in the case
       of sendmail(1), with the "-C" option), or via the MAIL_CONFIG  environ-
       ment parameter.

       This  list  must  be specified in the default Postfix main.cf file, and
       will be used by set-gid Postfix commands such as postqueue(1) and post-
       drop(1).

       Specify  absolute  pathnames,  separated by comma or space. Note: $name
       expansion is not supported.

always_add_missing_headers (default: no)
       Always add (Resent-) From:, To:, Date: or Message-ID: headers when  not
       present.   Postfix  2.6  and  later add these headers only when clients
       match  the  local_header_rewrite_clients  parameter  setting.   Earlier
       Postfix  versions  always add these headers; this may break DKIM signa-
       tures  that  cover  non-existent  headers.    The   undisclosed_recipi-
       ents_header  parameter  setting determines whether a To: header will be
       added.

always_bcc (default: empty)
       Optional address that receives a "blind carbon copy"  of  each  message
       that is received by the Postfix mail system.

       Note:  with Postfix 2.3 and later the BCC address is added as if it was
       specified with NOTIFY=NONE. The sender will not be  notified  when  the
       BCC  address  is undeliverable, as long as all down-stream software im-
       plements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will be notified when the
       BCC address is undeliverable.

       Note:  automatic  BCC  recipients  are  produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are  not  generated  after
       Postfix  forwards  mail internally, or after Postfix generates mail it-
       self.

anvil_rate_time_unit (default: 60s)
       The time unit over which client connection rates and  other  rates  are
       calculated.

       This  feature is implemented by the anvil(8) service which is available
       in Postfix version 2.2 and later.

       The default interval is relatively short. Because of the high frequency
       of updates, the anvil(8) server uses volatile memory only. Thus, infor-
       mation is lost whenever the process terminates.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

anvil_status_update_time (default: 600s)
       How  frequently  the  anvil(8) connection and rate limiting server logs
       peak usage information.

       This feature is available in Postfix 2.2 and later.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

append_at_myorigin (default: yes)
       With locally submitted mail, append the string "@$myorigin" to mail ad-
       dresses without domain information. With remotely submitted  mail,  ap-
       pend the string "@$remote_header_rewrite_domain" instead.

       Note  1: this feature is enabled by default and must not be turned off.
       Postfix does not support domain-less addresses.

       Note 2: with Postfix version 2.2, message header address rewriting hap-
       pens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The  message is received from a network client that matches $lo-
              cal_header_rewrite_clients,

       o      The  message  is  received  from  the  network,  and   the   re-
              mote_header_rewrite_domain   parameter   specifies  a  non-empty
              value.

       To  get  the  behavior  before  Postfix  version  2.2,   specify   "lo-
       cal_header_rewrite_clients = static:all".

append_dot_mydomain (default: Postfix >= 3.0: no, Postfix < 3.0: yes)
       With  locally  submitted  mail,  append  the string ".$mydomain" to ad-
       dresses that have no ".domain"  information.  With  remotely  submitted
       mail, append the string ".$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default. If disabled, users will not
       be able to send mail to "user@partialdomainname" but will have to spec-
       ify full domain names instead.

       Note 2: with Postfix version 2.2, message header address rewriting hap-
       pens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches  $lo-
              cal_header_rewrite_clients,

       o      The   message   is  received  from  the  network,  and  the  re-
              mote_header_rewrite_domain  parameter  specifies   a   non-empty
              value.

       To   get   the  behavior  before  Postfix  version  2.2,  specify  "lo-
       cal_header_rewrite_clients = static:all".

application_event_drain_time (default: 100s)
       How long the postkick(1) command waits for a request to enter the Post-
       fix daemon process input buffer before giving up.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
       List of users who are authorized to flush the queue.

       By default, all users are allowed to flush the queue.  Access is always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system pass-
       word  file,  and access is granted only if the corresponding login name
       is on the access list.  The username "unknown" is  used  for  processes
       whose real UID is not found in the password file.

       Specify  a  list  of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The  list  is  matched  left  to
       right,  and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con-
       tinue long lines by starting the next  line  with  whitespace.  Specify
       "!pattern"  to  exclude a name from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
       List of users who are authorized to view the queue.

       By default, all users are allowed to view the queue.  Access is  always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system pass-
       word  file,  and access is granted only if the corresponding login name
       is on the access list.  The username "unknown" is  used  for  processes
       whose real UID is not found in the password file.

       Specify  a  list  of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The  list  is  matched  left  to
       right,  and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con-
       tinue long lines by starting the next  line  with  whitespace.  Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
       List of users who are authorized to submit mail  with  the  sendmail(1)
       command (and with the privileged postdrop(1) helper command).

       By  default, all users are allowed to submit mail.  Otherwise, the real
       UID of the process is looked up in the system password file, and access
       is  granted only if the corresponding login name is on the access list.
       The username "unknown" is used for processes  whose  real  UID  is  not
       found in the password file. To deny mail submission access to all users
       specify an empty list.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by  its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).   Con-
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       Example:

       authorized_submit_users = !www, static:all

       This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
       What  remote  SMTP  clients  are  allowed to specify the XVERP command.
       This command requests that mail be delivered one recipient  at  a  time
       with a per recipient return address.

       By default, only trusted clients are allowed to specify XVERP.

       This  parameter  was introduced with Postfix version 1.1.  Postfix ver-
       sion 2.1 renamed this parameter  to  smtpd_authorized_verp_clients  and
       changed the default to none.

       Specify  a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the  network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial  dot  causes  the  domain  to  match  any   name   below   it),
       "/file/name"  or  "type:table" patterns.  A "/file/name" pattern is re-
       placed by its contents; a "type:table" lookup table is matched  when  a
       table  entry  matches  a  lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude  an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside  []  in
       the   authorized_verp_clients   value,  and  in  files  specified  with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

backwards_bounce_logfile_compatibility (default: yes)
       Produce  additional bounce(8) logfile records that can be read by Post-
       fix versions before 2.0. The current and more extensible "name = value"
       format  is  needed in order to implement more sophisticated functional-
       ity.

       This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
       The per-table I/O buffer size for programs that create Berkeley DB hash
       or btree tables.  Specify a byte count.

       This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
       The  per-table  I/O buffer size for programs that read Berkeley DB hash
       or btree tables.  Specify a byte count.

       This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
       Where the Postfix SMTP client should deliver mail  when  it  detects  a
       "mail  loops back to myself" error condition. This happens when the lo-
       cal MTA is the best SMTP mail exchanger for a destination not listed in
       $mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_do-
       mains, or  $virtual_mailbox_domains.   By  default,  the  Postfix  SMTP
       client returns such mail as undeliverable.

       Specify, for example, "best_mx_transport = local" to pass the mail from
       the Postfix SMTP client to the local(8) delivery agent. You can specify
       any message delivery "transport" or "transport:nexthop" that is defined
       in the master.cf file. See the transport(5) manual page for the  syntax
       and meaning of "transport" or "transport:nexthop".

       However,  this  feature  is expensive because it ties up a Postfix SMTP
       client process while the local(8) delivery agent is doing its work.  It
       is  more  efficient (for Postfix) to list all hosted domains in a table
       or database.

biff (default: yes)
       Whether or not to use the local biff service.  This service sends  "new
       mail"  notifications  to users who have requested new mail notification
       with the UNIX command "biff y".

       For compatibility reasons this feature is on by  default.   On  systems
       with  lots  of interactive users, the biff service can be a performance
       drain.  Specify "biff = no" in main.cf to disable.

body_checks (default: empty)
       Optional lookup tables for  content  inspection  as  specified  in  the
       body_checks(5) manual page.

       Note: with Postfix versions before 2.0, these rules inspect all content
       after the primary message headers.

body_checks_size_limit (default: 51200)
       How much text in a message body segment (or attachment, if  you  prefer
       to  use  that term) is subjected to body_checks inspection.  The amount
       of text is limited to avoid scanning huge attachments.

       This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message  headers  of
       mail  that Postfix did not deliver and of SMTP conversation transcripts
       of mail that Postfix did not receive.  This feature is enabled with the
       notify_classes parameter.

bounce_queue_lifetime (default: 5d)
       Consider  a bounce message as undeliverable, when delivery fails with a
       temporary  error,  and  the  time  in  the  queue   has   reached   the
       bounce_queue_lifetime limit.  By default, this limit is the same as for
       regular mail.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

       This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
       The  name  of the bounce(8) service. This service maintains a record of
       failed delivery attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
       The maximal amount of original message text that is sent in  a  non-de-
       livery  notification.  Specify  a byte count.  A message is returned as
       either message/rfc822 (the complete original) or as text/rfc822-headers
       (the headers only).  With Postfix version 2.4 and earlier, a message is
       always returned as message/rfc822 and is truncated when it exceeds  the
       size limit.

       Notes:

       o      If  you  increase  this  limit,  then  you  should  increase the
              mime_nesting_limit value proportionally.

       o      Be careful when making changes.  Excessively large  values  will
              result  in the loss of non-delivery notifications, when a bounce
              message size exceeds a local or remote MTA's message size limit.

bounce_template_file (default: empty)
       Pathname of a configuration file with bounce message templates.   These
       override  the  built-in templates of delivery status notification (DSN)
       messages for undeliverable mail, for delayed mail, successful delivery,
       or  delivery  verification.  The bounce(5) manual page describes how to
       edit and test template files.

       Template message body text may contain $name references to Postfix con-
       figuration  parameters.  The result of $name expansion can be previewed
       with "postconf -b file_name" before the file is placed into the Postfix
       configuration directory.

       This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
       Enable  interoperability with remote SMTP clients that implement an ob-
       solete version of the AUTH command (RFC 4954). Examples of such clients
       are  MicroSoft Outlook Express version 4 and MicroSoft Exchange version
       5.0.

       Specify "broken_sasl_auth_clients = yes" to have Postfix advertise AUTH
       support in a non-standard way.

canonical_classes      (default:      envelope_sender,     envelope_recipient,
       header_sender, header_recipient)
       What addresses are subject to canonical_maps address mapping.   By  de-
       fault, canonical_maps address mapping is applied to envelope sender and
       recipient addresses, and to header  sender  and  header  recipient  ad-
       dresses.

       Specify   one   or   more   of:   envelope_sender,  envelope_recipient,
       header_sender, header_recipient

       This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
       Optional address mapping lookup tables  for  message  headers  and  en-
       velopes. The mapping is applied to both sender and recipient addresses,
       in both envelopes and  in  headers,  as  controlled  with  the  canoni-
       cal_classes  parameter.  This  is  typically used to clean up dirty ad-
       dresses from legacy mail systems, or to replace login names  by  First-
       name.Lastname.   The table format and lookups are documented in canoni-
       cal(5). For an overview of Postfix address manipulations  see  the  AD-
       DRESS_REWRITING_README document.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.  Note: these lookups are recursive.

       If  you use this feature, run "postmap /etc/postfix/canonical" to build
       the necessary DBM or DB file after every change. The changes  will  be-
       come  visible  after a minute or so.  Use "postfix reload" to eliminate
       the delay.

       Note: with Postfix version 2.2, message header address mapping  happens
       only when message header address rewriting is enabled:

       o      The message is received with the Postfix sendmail(1) command,

       o      The  message is received from a network client that matches $lo-
              cal_header_rewrite_clients,

       o      The  message  is  received  from  the  network,  and   the   re-
              mote_header_rewrite_domain   parameter   specifies  a  non-empty
              value.

       To  get  the  behavior  before  Postfix  version  2.2,   specify   "lo-
       cal_header_rewrite_clients = static:all".

       Examples:

       canonical_maps = dbm:/etc/postfix/canonical
       canonical_maps = hash:/etc/postfix/canonical

cleanup_replace_stray_cr_lf (default: yes)
       Replace  each  stray  <CR>  or <LF> character in message content with a
       space character, to prevent outbound SMTP smuggling, and  to  make  the
       evaluation  of  Postfix-added DKIM or other signatures independent from
       how a remote mail server handles such characters.

       SMTP does not allow such characters unless they are part of a  <CR><LF>
       sequence, and different mail systems handle such stray characters in an
       implementation-dependent manner. Stray <CR> or <LF> characters could be
       used  for  outbound  SMTP  smuggling,  where an attacker uses a Postfix
       server to send message content with a non-standard End-of-DATA sequence
       that triggers inbound SMTP smuggling at a remote SMTP server.

       The replacement happens before all other content management, and before
       Postfix may add a DKIM etc. signature; if the  signature  were  created
       first, the replacement could invalidate the signature.

       In  addition to preventing SMTP smuggling, replacing stray <CR> or <LF>
       characters ensures that the result of  signature  validation  by  later
       mail system will not depend on how that mail system handles those stray
       characters in an implementation-dependent manner.

       This feature is available in Postfix >= 3.9, 3.8.5, 3.7.10, 3.6.14, and
       3.5.24.

cleanup_service_name (default: cleanup)
       The  name  of  the  cleanup(8) service. This service rewrites addresses
       into the standard form, and performs canonical(5) address  mapping  and
       virtual(5) aliasing.

       This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
       The location of all postfix administrative commands.

command_execution_directory (default: empty)
       The  local(8) delivery agent working directory for delivery to external
       command.  Failure to change directory causes the  delivery  to  be  de-
       ferred.

       The command_execution_directory value is not subject to Postfix config-
       uration parameter $name expansion. Instead, the following $name  expan-
       sions  are  done on command_execution_directory before the directory is
       used. Expansion happens in the context of the  delivery  request.   The
       result  of  $name  expansion is filtered with the character set that is
       specified with the execution_directory_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The address extension delimiter that was found in the  recipient
              address  (Postfix  2.11 and later), or the system-wide recipient
              address extension delimiter (Postfix 2.10 and earlier).

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
       Restrict the characters that the  local(8)  delivery  agent  allows  in
       $name  expansions of $mailbox_command and $command_execution_directory.
       Characters outside the allowed set are replaced by underscores.

command_time_limit (default: 1000s)
       Time limit for delivery to external commands. This limit is used by the
       local(8)  delivery agent, and is the default time limit for delivery by
       the pipe(8) delivery agent.

       Note: if you set this time limit to a large value you must  update  the
       global ipc_timeout parameter as well.

compatibility_level (default: 0)
       A  safety  net that causes Postfix to run with backwards-compatible de-
       fault settings after an upgrade to a newer Postfix version.

       With backwards compatibility turned on (the main.cf compatibility_level
       value  is less than the Postfix built-in value), Postfix looks for set-
       tings that are left at their implicit default value, and logs a message
       when a backwards-compatible default setting is required.

           using backwards-compatible default setting name=value
               to [accept a specific client request]

           using backwards-compatible default setting name=value
               to [enable specific Postfix behavior]

       See  COMPATIBILITY_README  for specific message details. If such a mes-
       sage is logged in the context of a legitimate request, the  system  ad-
       ministrator  should  make the backwards-compatible setting permanent in
       main.cf or master.cf, for example:

           # postconf name=value
           # postfix reload

       When no more backwards-compatible settings need to be  made  permanent,
       the  administrator  should turn off backwards compatibility by updating
       the compatibility_level setting in main.cf:

           # postconf compatibility_level=N
           # postfix reload

       For N specify the number that is logged in your postfix(1) warning mes-
       sage:

           warning: To disable backwards compatibility use "postconf
               compatibility_level=N" and "postfix reload"

       This feature is available in Postfix 3.0 and later.

config_directory (default: see postconf -d output)
       The default location of the Postfix main.cf and master.cf configuration
       files. This can be overruled via the following mechanisms:

       o      The MAIL_CONFIG environment variable (daemon processes and  com-
              mands).

       o      The "-c" command-line option (commands only).

       With  Postfix command that run with set-gid privileges, a config_direc-
       tory override requires either root privileges, or it requires that  the
       directory  is listed with the alternate_config_directories parameter in
       the default main.cf file.

confirm_delay_cleared (default: no)
       After sending a "your message  is  delayed"  notification,  inform  the
       sender  when  the delay clears up. This can result in a sudden burst of
       notifications at the end of a prolonged network outage, and  is  there-
       fore disabled by default.

       See also: delay_warning_time.

       This feature is available in Postfix 3.0 and later.

connection_cache_protocol_timeout (default: 5s)
       Time  limit  for  connection cache connect, send or receive operations.
       The time limit is enforced in the client.

       This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)
       The name of the scache(8) connection cache service.  This service main-
       tains a limited pool of cached sessions.

       This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)
       How  frequently the scache(8) server logs usage statistics with connec-
       tion cache hit and miss rates for logical destinations and for physical
       endpoints.

connection_cache_ttl_limit (default: 2s)
       The  maximal  time-to-live  value  that  the scache(8) connection cache
       server allows. Requests that specify a larger TTL will be  stored  with
       the  maximum  allowed TTL. The purpose of this additional control is to
       protect the infrastructure against careless people. The  cache  TTL  is
       already bounded by $max_idle.

content_filter (default: empty)
       After  the  message is queued, send the entire message to the specified
       transport:destination. The transport name specifies the first field  of
       a  mail  delivery  agent  definition  in  master.cf;  the syntax of the
       next-hop destination is described in the manual page of the correspond-
       ing delivery agent.  More information about external content filters is
       in the Postfix FILTER_README file.

       Notes:

       o      This setting has lower precedence than a FILTER action  that  is
              specified  in  an  access(5), header_checks(5) or body_checks(5)
              table.

       o      The meaning of an empty next-hop filter destination  is  version
              dependent.  Postfix 2.7 and later will use the recipient domain;
              earlier versions will use  $myhostname.   Specify  "default_fil-
              ter_nexthop = $myhostname" for compatibility with Postfix 2.6 or
              earlier, or specify a  content_filter  value  with  an  explicit
              next-hop destination.

cyrus_sasl_config_path (default: empty)
       Search  path  for Cyrus SASL application configuration files, currently
       used only to locate the $smtpd_sasl_path.conf file.   Specify  zero  or
       more  directories  separated by a colon character, or an empty value to
       use Cyrus SASL's built-in search path.

       This feature is available in Postfix 2.5 and later when  compiled  with
       Cyrus SASL 2.1.22 or later.

daemon_directory (default: see postconf -d output)
       The directory with Postfix support programs and daemon programs.  These
       should not be invoked directly by humans. The directory must  be  owned
       by root.

daemon_table_open_error_is_fatal (default: no)
       How  a  Postfix  daemon process handles errors while opening lookup ta-
       bles: gradual degradation or immediate termination.

        no  (default)
              Gradual degradation: a daemon process logs  a  message  of  type
              "error" and continues execution with reduced functionality. Fea-
              tures that do not depend on the unavailable table will work nor-
              mally,  while features that depend on the table will result in a
              type "warning" message.
              When the notify_classes  parameter  value  contains  the  "data"
              class,  the  Postfix  SMTP  server  and client will report tran-
              scripts of sessions with an error because a  table  is  unavail-
              able.

        yes  (historical behavior)
              Immediate termination: a daemon process logs a type "fatal" mes-
              sage and terminates immediately.  This option reduces the number
              of  possible  code  paths  through Postfix, and may therefore be
              slightly more secure than the default.

       For the sake of sanity, the number of type "error" messages is  limited
       to 13 over the lifetime of a daemon process.

       This feature is available in Postfix 2.9 and later.

daemon_timeout (default: 18000s)
       How much time a Postfix daemon process may take to handle a request be-
       fore it is terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

data_directory (default: see postconf -d output)
       The  directory  with  Postfix-writable data files (for example: caches,
       pseudo-random numbers).  This directory must be owned by the mail_owner
       account, and must not be shared with non-Postfix software.

       This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)
       The  increment  in verbose logging level when a remote client or server
       matches a pattern in the debug_peer_list parameter.

debug_peer_list (default: empty)
       Optional list of remote client or server hostname  or  network  address
       patterns that cause the verbose logging level to increase by the amount
       specified in $debug_peer_level.

       Specify domain names, network/netmask patterns,  "/file/name"  patterns
       or   "type:table"  lookup  tables.  The  right-hand  side  result  from
       "type:table" lookups is ignored.

       Pattern matching of domain names is controlled by the presence  or  ab-
       sence  of "debug_peer_list" in the parent_domain_matches_subdomains pa-
       rameter value.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = example.com

debugger_command (default: empty)
       The external command to execute when a Postfix daemon  program  is  in-
       voked with the -D option.

       Use  "command  .. & sleep 5" so that the debugger can attach before the
       process marches on. If you use an X-based debugger, be sure to  set  up
       your XAUTHORITY environment variable before starting Postfix.

       Note: the command is subject to $name expansion, before it is passed to
       the default command interpreter. Specify "$$" to produce a  single  "$"
       character.

       Example:

       debugger_command =
           PATH=/usr/bin:/usr/X11R6/bin
           ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
       The  default  database  type for use in newaliases(1), postalias(1) and
       postmap(1) commands. On many UNIX systems the default  type  is  either
       dbm  or  hash. The default setting is frozen when the Postfix system is
       built.

       Examples:

       default_database_type = hash
       default_database_type = dbm

default_delivery_slot_cost (default: 5)
       How often the Postfix queue manager's scheduler is allowed  to  preempt
       delivery of one message with another.

       Each  transport maintains a so-called "available delivery slot counter"
       for each message. One message can be preempted by another one when  the
       other  message can be delivered using no more delivery slots (i.e., in-
       vocations of delivery agents) than the current message counter has  ac-
       cumulated (or will eventually accumulate - see about slot loans below).
       This parameter controls how often is the counter incremented - it  hap-
       pens  after each default_delivery_slot_cost recipients have been deliv-
       ered.

       The cost of 0 is used to disable the preempting scheduling  completely.
       The minimum value the scheduling algorithm can use is 2 - use it if you
       want to maximize the message throughput rate. Although there is no max-
       imum, it doesn't make much sense to use values above say 50.

       The  only  reason why the value of 2 is not the default is the way this
       parameter affects the delivery of mailing-list mail. In the worst case,
       delivery  can  take  somewhere  between (cost+1/cost) and (cost/cost-1)
       times more than if the preemptive scheduler was disabled.  The  default
       value of 5 turns out to provide reasonable message response times while
       making sure the mailing-list deliveries are not extended by  more  than
       20-25 percent even in the worst case.

       Use  transport_delivery_slot_cost to specify a transport-specific over-
       ride, where transport is the master.cf name  of  the  message  delivery
       transport.

       Examples:

       default_delivery_slot_cost = 0
       default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
       The  default  value for transport-specific _delivery_slot_discount set-
       tings.

       This parameter speeds up the moment when a message preemption can  hap-
       pen.  Instead  of  waiting  until the full amount of delivery slots re-
       quired is available, the preemption can  happen  when  transport_deliv-
       ery_slot_discount  percent of the required amount plus transport_deliv-
       ery_slot_loan still remains to be  accumulated.   Note  that  the  full
       amount  will still have to be accumulated before another preemption can
       take place later.

       Use transport_delivery_slot_discount to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_delivery_slot_loan (default: 3)
       The default value for transport-specific _delivery_slot_loan settings.

       This parameter speeds up the moment when a message preemption can  hap-
       pen.  Instead  of  waiting  until the full amount of delivery slots re-
       quired is available, the preemption can  happen  when  transport_deliv-
       ery_slot_discount  percent of the required amount plus transport_deliv-
       ery_slot_loan still remains to be  accumulated.   Note  that  the  full
       amount  will still have to be accumulated before another preemption can
       take place later.

       Use transport_delivery_slot_loan to specify a transport-specific  over-
       ride,  where  transport  is  the master.cf name of the message delivery
       transport.

default_delivery_status_filter (default: empty)
       Optional filter to replace the delivery status code or explanatory text
       of  successful or unsuccessful deliveries.  This does not allow the re-
       placement of a successful status code (2.X.X) with an unsuccessful sta-
       tus code (4.X.X or 5.X.X) or vice versa.

       Note:  the  (smtp|lmtp)_delivery_status_filter is applied only once per
       recipient: when delivery is successful, when delivery is rejected  with
       5XX,  or  when  there  are  no more alternate MX or A destinations. Use
       smtp_reply_filter or lmtp_reply_filter to inspect responses for all de-
       livery attempts.

       The following parameters can be used to implement a filter for specific
       delivery   agents:   lmtp_delivery_status_filter,   local_delivery_sta-
       tus_filter, pipe_delivery_status_filter, smtp_delivery_status_filter or
       virtual_delivery_status_filter. These parameters support the same  fil-
       ter syntax as described here.

       Specify  zero  or  more  "type:table"  lookup table names, separated by
       comma or whitespace. For each successful or unsuccessful delivery to  a
       recipient,  the tables are queried in the specified order with one line
       of text that is structured as follows:

           enhanced-status-code SPACE explanatory-text

       The first table match wins. The lookup result must have the same struc-
       ture  as  the  query, a successful status code (2.X.X) must be replaced
       with a successful status code, an unsuccessful status  code  (4.X.X  or
       5.X.X)  must  be replaced with an unsuccessful status code, and the ex-
       planatory text field must be non-empty. Other results will result in  a
       warning.

       Example  1: convert specific soft TLS errors into hard errors, by over-
       riding the first number in the enhanced status code.

           /etc/postfix/main.cf:
               smtp_delivery_status_filter = pcre:/etc/postfix/smtp_dsn_filter

           /etc/postfix/smtp_dsn_filter:
               /^4(\.\d+\.\d+ TLS is required, but host \S+ refused to start TLS: .+)/
                   5$1
               /^4(\.\d+\.\d+ TLS is required, but was not offered by host .+)/
                   5$1
               # Do not change the following into hard bounces. They may
               # result from a local configuration problem.
               # 4.\d+.\d+ TLS is required, but our TLS engine is unavailable
               # 4.\d+.\d+ TLS is required, but unavailable
               # 4.\d+.\d+ Cannot start TLS: handshake failure

       Example 2: censor the per-recipient delivery status  text  so  that  it
       does  not  reveal  the  destination  command  or filename when a remote
       sender requests confirmation of successful delivery.

           /etc/postfix/main.cf:
               local_delivery_status_filter = pcre:/etc/postfix/local_dsn_filter

           /etc/postfix/local_dsn_filter:
               /^(2\S+ delivered to file).+/    $1
               /^(2\S+ delivered to command).+/ $1

       Notes:

       o      This feature will NOT override the soft_bounce safety net.

       o      This feature will change the enhanced status code and text  that
              is  logged  to  the  maillog  file,  and that is reported to the
              sender in delivery confirmation or non-delivery notifications.

       This feature is available in Postfix 3.0 and later.

default_destination_concurrency_failed_cohort_limit (default: 1)
       How many pseudo-cohorts must suffer connection or handshake failure be-
       fore  a specific destination is considered unavailable (and further de-
       livery is suspended). Specify zero to disable this feature. A  destina-
       tion's  pseudo-cohort  failure count is reset each time a delivery com-
       pletes without connection or handshake failure for that specific desti-
       nation.

       A  pseudo-cohort  is  the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_failed_cohort_limit to specify  a
       transport-specific  override,  where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5. The default setting  is  com-
       patible with earlier Postfix versions.

default_destination_concurrency_limit (default: 20)
       The  default maximal number of parallel deliveries to the same destina-
       tion.  This is the default limit for delivery via the lmtp(8), pipe(8),
       smtp(8) and virtual(8) delivery agents.  With per-destination recipient
       limit > 1, a destination is a domain, otherwise it is a recipient.

       Use transport_destination_concurrency_limit to specify a transport-spe-
       cific  override,  where  transport is the master.cf name of the message
       delivery transport.

default_destination_concurrency_negative_feedback (default: 1)
       The per-destination amount of delivery concurrency  negative  feedback,
       after  a  delivery  completes  with  a connection or handshake failure.
       Feedback values are in the range 0..1 inclusive.  With  negative  feed-
       back,  concurrency  is  decremented  at  the beginning of a sequence of
       length 1/feedback. This is unlike positive feedback, where  concurrency
       is incremented at the end of a sequence of length 1/feedback.

       As  of  Postfix  version  2.5, negative feedback cannot reduce delivery
       concurrency to zero.  Instead, a destination is  marked  dead  (further
       delivery  suspended)  after the failed pseudo-cohort count reaches $de-
       fault_destination_concurrency_failed_cohort_limit (or $transport_desti-
       nation_concurrency_failed_cohort_limit).   To  make  the scheduler com-
       pletely immune to connection or  handshake  failures,  specify  a  zero
       feedback value and a zero failed pseudo-cohort limit.

       Specify one of the following forms:

       number

       number / number
              Constant  feedback.  The  value must be in the range 0..1 inclu-
              sive.  The default setting of "1"  is  compatible  with  Postfix
              versions  before 2.5, where a destination's delivery concurrency
              is throttled down to zero (and further delivery suspended) after
              a single failed pseudo-cohort.

       number / concurrency
              Variable  feedback  of  "number  / (delivery concurrency)".  The
              number must be in the range 0..1 inclusive. With number equal to
              "1",  a  destination's  delivery concurrency is decremented by 1
              after each failed pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal  to  a  destination's
       delivery concurrency.

       Use  transport_destination_concurrency_negative_feedback  to  specify a
       transport-specific override, where transport is the master.cf  name  of
       the message delivery transport.

       This  feature  is available in Postfix 2.5. The default setting is com-
       patible with earlier Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)
       The per-destination amount of delivery concurrency  positive  feedback,
       after  a  delivery  completes  without connection or handshake failure.
       Feedback values are in the range 0..1 inclusive.  The  concurrency  in-
       creases until it reaches the per-destination maximal concurrency limit.
       With positive feedback, concurrency is incremented at the end of a  se-
       quence  with length 1/feedback. This is unlike negative feedback, where
       concurrency is decremented at the start of a sequence of length 1/feed-
       back.

       Specify one of the following forms:

       number

       number / number
              Constant  feedback.   The value must be in the range 0..1 inclu-
              sive. The default setting of "1" is compatible with Postfix ver-
              sions  before  2.5,  where  a destination's delivery concurrency
              doubles after each successful pseudo-cohort.

       number / concurrency
              Variable feedback of "number  /  (delivery  concurrency)".   The
              number must be in the range 0..1 inclusive. With number equal to
              "1", a destination's delivery concurrency is  incremented  by  1
              after each successful pseudo-cohort.

       A  pseudo-cohort  is  the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_positive_feedback  to  specify  a
       transport-specific  override,  where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)
       The default amount of delay that is inserted between individual message
       deliveries  to  the same destination and over the same message delivery
       transport. Specify a non-zero value to rate-limit those message  deliv-
       eries to at most one per $default_destination_rate_delay.

       The  resulting  behavior  depends  on  the  value  of the corresponding
       per-destination recipient limit.

       o      With a corresponding per-destination recipient limit  >  1,  the
              rate delay specifies the time between deliveries to the same do-
              main.  Different domains are delivered in parallel,  subject  to
              the process limits specified in master.cf.

       o      With a corresponding per-destination recipient limit equal to 1,
              the rate delay specifies the time between deliveries to the same
              recipient.  Different recipients are delivered in parallel, sub-
              ject to the process limits specified in master.cf.

       To enable the delay, specify a non-zero time value (an  integral  value
       plus an optional one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       NOTE: the delay is enforced by the queue manager. The delay timer state
       does not survive "postfix reload" or "postfix stop".

       Use  transport_destination_rate_delay  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       NOTE: with a non-zero _destination_rate_delay, specify a transport_des-
       tination_concurrency_failed_cohort_limit of 10 or more to prevent Post-
       fix  from  deferring  all  mail for the same destination after only one
       connection or handshake error.

       This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)
       The default maximal number of recipients per message delivery.  This is
       the  default  limit  for delivery via the lmtp(8), pipe(8), smtp(8) and
       virtual(8) delivery agents.

       Setting this parameter to a value of 1 affects email deliveries as fol-
       lows:

       o      It changes the meaning of the corresponding per-destination con-
              currency limit, from concurrency of deliveries to the  same  do-
              main into concurrency of deliveries to the same recipient.  Dif-
              ferent recipients are delivered  in  parallel,  subject  to  the
              process limits specified in master.cf.

       o      It changes the meaning of the corresponding per-destination rate
              delay, from the delay between deliveries to the same domain into
              the delay between deliveries to the same recipient.  Again, dif-
              ferent recipients are delivered  in  parallel,  subject  to  the
              process limits specified in master.cf.

       o      It  changes  the  meaning of other corresponding per-destination
              settings in a similar manner, from settings for delivery to  the
              same domain into settings for delivery to the same recipient.

       Use  transport_destination_recipient_limit  to specify a transport-spe-
       cific override, where transport is the master.cf name  of  the  message
       delivery transport.

default_extra_recipient_limit (default: 1000)
       The default value for the extra per-transport limit imposed on the num-
       ber of in-memory recipients.  This extra recipient  space  is  reserved
       for  the  cases when the Postfix queue manager's scheduler preempts one
       message with another and suddenly needs some extra recipients slots for
       the chosen message in order to avoid performance degradation.

       Use  transport_extra_recipient_limit  to  specify  a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_filter_nexthop (default: empty)
       When  a content_filter or FILTER request specifies no explicit next-hop
       destination, use $default_filter_nexthop instead; when  that  value  is
       empty,  use the domain in the recipient address.  Specify "default_fil-
       ter_nexthop = $myhostname" for compatibility with Postfix  version  2.6
       and earlier, or specify an explicit next-hop destination with each con-
       tent_filter value or FILTER action.

       This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)
       How many recipients a message must have in order to invoke the  Postfix
       queue  manager's  scheduling  algorithm  at  all.  Messages which would
       never accumulate at least this many delivery  slots  (subject  to  slot
       cost parameter as well) are never preempted.

       Use  transport_minimum_delivery_slots  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_privs (default: nobody)
       The  default rights used by the local(8) delivery agent for delivery to
       external file or command.  These rights are used when delivery  is  re-
       quested from an aliases(5) file that is owned by root, or when delivery
       is done on behalf of root. DO NOT SPECIFY  A  PRIVILEGED  USER  OR  THE
       POSTFIX OWNER.

default_process_limit (default: 100)
       The  default  maximal  number of Postfix child processes that provide a
       given service. This limit can be overruled for specific services in the
       master.cf file.

default_rbl_reply (default: see postconf -d output)
       The default Postfix SMTP server response template for a request that is
       rejected by an RBL-based restriction. This template can be overruled by
       specific entries in the optional rbl_reply_maps lookup table.

       This feature is available in Postfix 2.0 and later.

       The  template  does  not  support Postfix configuration parameter $name
       substitution. Instead, it supports exactly one level of $name substitu-
       tion for the following attributes:

       $client
              The client hostname and IP address, formatted as name[address].

       $client_address
              The client IP address.

       $client_name
              The    client    hostname    or    "unknown".   See   reject_un-
              known_client_hostname for more details.

       $reverse_client_name
              The client hostname from  address->name  lookup,  or  "unknown".
              See reject_unknown_reverse_client_hostname for more details.

       $helo_name
              The hostname given in HELO or EHLO command or empty string.

       $rbl_class
              The  blacklisted  entity type: Client host, Helo command, Sender
              address, or Recipient address.

       $rbl_code
              The  numerical  SMTP  response  code,  as  specified  with   the
              maps_rbl_reject_code  configuration parameter. Note: The numeri-
              cal SMTP response code is required, and must appear at the start
              of  the  reply. With Postfix version 2.3 and later this informa-
              tion may be followed by an RFC 3463 enhanced status code.

       $rbl_domain
              The RBL domain where $rbl_what is blacklisted.

       $rbl_reason
              The reason why $rbl_what is blacklisted, or an empty string.

       $rbl_what
              The entity that is blacklisted (an IP address, a hostname, a do-
              main name, or an email address whose domain was blacklisted).

       $recipient
              The recipient address or <> in case of the null address.

       $recipient_domain
              The recipient domain or empty string.

       $recipient_name
              The recipient address localpart or <> in case of null address.

       $sender
              The sender address or <> in case of the null address.

       $sender_domain
              The sender domain or empty string.

       $sender_name
              The sender address localpart or <> in case of the null address.

       ${name?text}
              Expands to `text' if $name is not empty.

       ${name:text}
              Expands to `text' if $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Note:  when  an  enhanced status code is specified in an RBL reply tem-
       plate, it is subject to modification.   The  following  transformations
       are  needed  when the same RBL reply template is used for client, helo,
       sender, or recipient access restrictions.

       o      When rejecting a sender address, the Postfix  SMTP  server  will
              transform  a  recipient  DSN status (e.g., 4.1.1-4.1.6) into the
              corresponding sender DSN status, and vice versa.

       o      When rejecting non-address information (such as the HELO command
              argument  or  the  client  hostname/address),  the  Postfix SMTP
              server will transform a sender or recipient DSN  status  into  a
              generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
       The default per-transport upper limit on the number of in-memory recip-
       ients.  These limits take priority over the global qmgr_message_recipi-
       ent_limit  after the message has been assigned to the respective trans-
       ports.  See also default_extra_recipient_limit and qmgr_message_recipi-
       ent_minimum.

       Use transport_recipient_limit to specify a transport-specific override,
       where transport is the master.cf name of the  message  delivery  trans-
       port.

default_recipient_refill_delay (default: 5s)
       The  default  per-transport  maximum  delay between recipients refills.
       When not all message recipients fit into the memory at once, keep load-
       ing  more  of them at least once every this many seconds.  This is used
       to make sure the recipients are refilled in  timely  manner  even  when
       $default_recipient_refill_limit is too high for too slow deliveries.

       Use  transport_recipient_refill_delay  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)
       The default per-transport limit on the number of recipients refilled at
       once.  When not all message recipients fit into  the  memory  at  once,
       keep  loading  more of them in batches of at least this many at a time.
       See also $default_recipient_refill_delay, which may result in recipient
       batches lower than this when this limit is too high for too slow deliv-
       eries.

       Use transport_recipient_refill_limit to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)
       The default mail delivery transport and next-hop destination for desti-
       nations  that do not match $mydestination, $inet_interfaces, $proxy_in-
       terfaces,  $virtual_alias_domains,  $virtual_mailbox_domains,  or  $re-
       lay_domains.   This information can be overruled with the sender_depen-
       dent_default_transport_maps parameter and with the transport(5) table.

       In order of decreasing precedence, the  nexthop  destination  is  taken
       from    $sender_dependent_default_transport_maps,   $default_transport,
       $sender_dependent_relayhost_maps, $relayhost, or from the recipient do-
       main.

       Specify  a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.   The  :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Example:

       default_transport = uucp:relayhostname

default_transport_rate_delay (default: 0s)
       The default amount of delay that is inserted between individual message
       deliveries over the same message delivery transport, regardless of des-
       tination. Specify a non-zero value to rate-limit those message deliver-
       ies to at most one per $default_transport_rate_delay.

       Use  transport_transport_rate_delay  to  specify  a  transport-specific
       override, where the initial transport is the master.cf name of the mes-
       sage delivery transport.

       Example:  throttle  outbound  SMTP  mail  to  at  most 3 deliveries per
       minute.

       /etc/postfix/main.cf:
           smtp_transport_rate_delay = 20s

       To enable the delay, specify a non-zero time value (an  integral  value
       plus an optional one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       NOTE: the delay is enforced by the queue manager.

       This feature is available in Postfix 3.1 and later.

default_verp_delimiters (default: +=)
       The two default VERP delimiter characters. These are used when  no  ex-
       plicit delimiters are specified with the SMTP XVERP command or with the
       "sendmail -V" command-line option. Specify characters that are  allowed
       by the verp_delimiter_filter setting.

       This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
       The  numerical  Postfix  SMTP  server  response code when a remote SMTP
       client request is rejected by the "defer" restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

defer_service_name (default: defer)
       The  name  of  the  defer  service.  This service is implemented by the
       bounce(8) daemon and maintains a record of failed delivery attempts and
       generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
       The  names  of message delivery transports that should not deliver mail
       unless someone issues "sendmail -q" or equivalent. Specify zero or more
       names  of mail delivery transports names that appear in the first field
       of master.cf.

       Example:

       defer_transports = smtp

delay_logging_resolution_limit (default: 2)
       The maximal number of digits  after  the  decimal  point  when  logging
       sub-second delay values.  Specify a number in the range 0..6.

       Large delay values are rounded off to an integral number seconds; delay
       values below the delay_logging_resolution_limit are logged as "0",  and
       delay values under 100s are logged with at most two-digit precision.

       The format of the "delays=a/b/c/d" logging is as follows:

       o      a = time from message arrival to last active queue entry

       o      b = time from last active queue entry to connection setup

       o      c = time in connection setup, including DNS, EHLO and STARTTLS

       o      d = time in message transmission

       This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
       The  recipient  of postmaster notifications with the message headers of
       mail that cannot be delivered within $delay_warning_time time units.

       See also: delay_warning_time, notify_classes.

delay_warning_time (default: 0h)
       The time after which the sender receives a copy of the message  headers
       of  mail that is still queued. The confirm_delay_cleared parameter con-
       trols sender notification when the delay clears up.

       To enable this feature, specify a  non-zero  time  value  (an  integral
       value plus an optional one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is h (hours).

       See   also:   delay_notice_recipient,    notify_classes,    confirm_de-
       lay_cleared.

deliver_lock_attempts (default: 20)
       The  maximal number of attempts to acquire an exclusive lock on a mail-
       box file or bounce(8) logfile.

deliver_lock_delay (default: 1s)
       The time between attempts to acquire an exclusive  lock  on  a  mailbox
       file or bounce(8) logfile.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

destination_concurrency_feedback_debug (default: no)
       Make the queue manager's feedback  algorithm  verbose  for  performance
       analysis purposes.

       This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)
       Automatically detect 8BITMIME body content by looking at Content-Trans-
       fer-Encoding:  message  headers;  historically,   this   behavior   was
       hard-coded to be "always on".

       This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)
       Disable  DNS  lookups  in  the Postfix SMTP and LMTP clients. When dis-
       abled, hosts are looked up with the getaddrinfo() system  library  rou-
       tine which normally also looks in /etc/hosts.  As of Postfix 2.11, this
       parameter is deprecated; use smtp_dns_support_level instead.

       DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
       Turn off MIME processing while receiving mail. This means that no  spe-
       cial  treatment is given to Content-Type: message headers, and that all
       text after the initial message headers is considered to be part of  the
       message body.

       This feature is available in Postfix 2.0 and later.

       Mime  input processing is enabled by default, and is needed in order to
       recognize MIME headers in message content.

disable_mime_output_conversion (default: no)
       Disable the conversion of 8BITMIME format to 7BIT format.  Mime  output
       conversion  is  needed when the destination does not advertise 8BITMIME
       support.

       This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
       Disable sending one bounce report per recipient.

       The default, one per recipient, is what ezmlm needs.

       This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
       Disable the SMTP VRFY command. This stops some techniques used to  har-
       vest email addresses.

       Example:

       disable_vrfy_command = no

dns_ncache_ttl_fix_enable (default: no)
       Enable a workaround for future libc incompatibility. The Postfix imple-
       mentation of RFC 2308 negative reply caching relies on the promise that
       res_query()  and  res_search()  invoke  res_send(),  which  returns the
       server response in an application buffer even if the  requested  record
       does  not  exist.  If this promise is broken, specify "yes" to enable a
       workaround for DNS reputation lookups.

       This feature is available in Postfix 3.1 and later.

dnsblog_reply_delay (default: 0s)
       A debugging aid to artificially delay DNS responses.

       This feature is available in Postfix 2.8.

dnsblog_service_name (default: dnsblog)
       The name of the dnsblog(8) service entry  in  master.cf.  This  service
       performs DNS white/blacklist lookups.

       This feature is available in Postfix 2.8 and later.

dont_remove (default: 0)
       Don't remove queue files and save them to the "saved" mail queue.  This
       is a debugging aid.  To inspect the envelope information and content of
       a Postfix queue file, use the postcat(1) command.

double_bounce_sender (default: double-bounce)
       The  sender  address  of postmaster notifications that are generated by
       the mail system. All mail to this address is silently discarded, in or-
       der to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
       The  maximal  number  of  addresses remembered by the address duplicate
       filter for aliases(5) or virtual(5) alias expansion,  or  for  showq(8)
       queue displays.

empty_address_default_transport_maps_lookup_key (default: <>)
       The  sender_dependent_default_transport_maps search string that will be
       used instead of the null sender address.

       This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)
       The recipient of mail addressed to the null address.  Postfix does  not
       accept  such  addresses in SMTP commands, but they may still be created
       locally as the result of configuration or software error.

empty_address_relayhost_maps_lookup_key (default: <>)
       The sender_dependent_relayhost_maps search string that will be used in-
       stead of the null sender address.

       This  feature  is available in Postfix 2.5 and later. With earlier ver-
       sions, sender_dependent_relayhost_maps lookups  were  skipped  for  the
       null sender address.

enable_errors_to (default: no)
       Report mail delivery errors to the address specified with the non-stan-
       dard Errors-To: message header, instead of the envelope sender  address
       (this feature is removed with Postfix version 2.2, is turned off by de-
       fault with Postfix version 2.1, and is  always  turned  on  with  older
       Postfix versions).

enable_idna2003_compatibility (default: no)
       Enable 'transitional' compatibility between IDNA2003 and IDNA2008, when
       converting UTF-8 domain names to/from the ASCII form that is  used  for
       DNS  lookups.  Specify "yes" for compatibility with Postfix <= 3.1 (not
       recommended). This affects the conversion of domain names that  contain
       for  example  the  German  sz  and  the  Greek  zeta.   See http://uni-
       code.org/cldr/utility/idna.jsp for more examples.

       This feature is available in Postfix 3.2 and later.

enable_long_queue_ids (default: no)
       Enable long, non-repeating, queue IDs (queue file names).  The  benefit
       of non-repeating names is simpler logfile analysis and easier queue mi-
       gration (there is no need to run "postsuper" to change queue file names
       that don't match their message file inode number).

       Note:  see below for how to convert long queue file names to Postfix <=
       2.8.

       Changing the parameter value to "yes" has the following effects:

       o      Existing queue file names are not affected.

       o      New queue files are created with names such as  3Pt2mN2VXxznjll.
              These  are encoded in a 52-character alphabet that contains dig-
              its (0-9),  upper-case  letters  (B-Z)  and  lower-case  letters
              (b-z).  For  safety reasons the vowels (AEIOUaeiou) are excluded
              from the alphabet.  The name format is: 6 or more characters for
              the  time in seconds, 4 characters for the time in microseconds,
              the 'z'; the remainder is the file inode number encoded  in  the
              first 51 characters of the 52-character alphabet.

       o      New messages have a Message-ID header with queueID@myhostname.

       o      The  mailq  (postqueue  -p)  output has a wider Queue ID column.
              The number of whitespace-separated fields is not changed.

       o      The hash_queue_depth algorithm uses the first characters of  the
              queue  file creation time in microseconds, after conversion into
              hexadecimal representation. This produces the same queue hashing
              behavior  as  if  the  queue  file  name  was  created with "en-
              able_long_queue_ids = no".

       Changing the parameter value to "no" has the following effects:

       o      Existing long queue file names are renamed  to  the  short  form
              (while running "postfix reload" or "postsuper").

       o      New  queue files are created with names such as C3CD21F3E90 from
              a hexadecimal alphabet that contains digits (0-9) and upper-case
              letters  (A-F). The name format is: 5 characters for the time in
              microseconds; the remainder is the file inode number.

       o      New  messages  have  a  Message-ID   header   with   YYYYMMDDHH-
              MMSS.queueid@myhostname,  where  YYYYMMDDHHMMSS  are  the  year,
              month, day, hour, minute and second.

       o      The mailq (postqueue -p) output has  the  same  format  as  with
              Postfix <= 2.8.

       o      The  hash_queue_depth algorithm uses the first characters of the
              queue file name, with the hexadecimal representation of the file
              creation time in microseconds.

       Before migration to Postfix <= 2.8, the following commands are required
       to convert long queue file names into short names:

       # postfix stop
       # postconf enable_long_queue_ids=no
       # postsuper

       Repeat the postsuper command until it reports no more queue  file  name
       changes.

       This feature is available in Postfix 2.9 and later.

enable_original_recipient (default: yes)
       Enable  support  for the original recipient address after an address is
       rewritten to a different address (for example  with  aliasing  or  with
       canonical mapping).

       The original recipient address is used as follows:

       Final delivery
              With  "enable_original_recipient  = yes", the original recipient
              address is stored in  the  X-Original-To  message  header.  This
              header  may  be used to distinguish between different recipients
              that share the same mailbox.

       Recipient deduplication
              With "enable_original_recipient = yes",  the  cleanup(8)  daemon
              performs duplicate recipient elimination based on the content of
              (original recipient, maybe-rewritten recipient)  pairs.   Other-
              wise,  the cleanup(8) daemon performs duplicate recipient elimi-
              nation based only on the maybe-rewritten recipient address.

       Note: with Postfix <= 3.2 the "setting enable_original_recipient =  no"
       breaks address verification for addresses that are aliased or otherwise
       rewritten (Postfix is unable to store the address  verification  result
       under the original probe destination address; instead, it can store the
       result only under the rewritten address).

       This feature is available in Postfix 2.1 and later. Postfix version 2.0
       behaves  as  if  this parameter is always set to yes.  Postfix versions
       before 2.0 have no support for the original recipient address.

error_notice_recipient (default: postmaster)
       The recipient of postmaster notifications about mail delivery  problems
       that  are  caused  by  policy,  resource,  software or protocol errors.
       These notifications are enabled with the notify_classes parameter.

error_service_name (default: error)
       The name of the error(8) pseudo delivery agent. This service always re-
       turns mail as undeliverable.

       This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
       Restrict  the  characters  that  the  local(8) delivery agent allows in
       $name expansions of $command_execution_directory.   Characters  outside
       the allowed set are replaced by underscores.

       This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
       When  delivering  to an alias "aliasname" that has an "owner-aliasname"
       companion alias, set the envelope sender address to  the  expansion  of
       the  "owner-aliasname"  alias.   Normally,  Postfix  sets  the envelope
       sender address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
       The list of environment variables that a Postfix process will export to
       non-Postfix  processes. The TZ variable is needed for sane time keeping
       on System-V-ish systems.

       Specify a list of names and/or name=value pairs,  separated  by  white-
       space or comma. Specify "{ name=value }" to protect whitespace or comma
       in parameter values (whitespace after the opening "{"  and  before  the
       closing  "}" is ignored). The form name=value is supported with Postfix
       version 2.1 and later; the use of {} is supported with Postfix 3.0  and
       later.

       Example:

       export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
       The  maximal  number  of  recipient addresses that Postfix will extract
       from message headers when mail is submitted with "sendmail -t".

       This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
       Optional list of relay hosts for SMTP destinations that can't be  found
       or  that are unreachable. With Postfix 2.3 this parameter is renamed to
       smtp_fallback_relay.

       By default, mail is returned to the sender when a  destination  is  not
       found, and delivery is deferred when a destination is unreachable.

       The  fallback relays must be SMTP destinations. Specify a domain, host,
       host:port, [host]:port, [address] or [address]:port;  the  form  [host]
       turns off MX lookups.  If you specify multiple SMTP destinations, Post-
       fix will try them in the specified order.

       Note: before Postfix 2.2, do not use the  fallback_relay  feature  when
       relaying  mail  for  a backup or primary MX domain. Mail would loop be-
       tween the Postfix MX host and the fallback_relay host  when  the  final
       destination is unavailable.

       o      In main.cf specify "relay_transport = relay",

       o      In  master.cf specify "-o fallback_relay =" (i.e., empty) at the
              end of the relay entry.

       o      In transport maps, specify "relay:nexthop..."  as the right-hand
              side for backup or primary MX domain entries.

       Postfix  version  2.2 and later will not use the fallback_relay feature
       for destinations that it is MX host for.

fallback_transport (default: empty)
       Optional message delivery transport that the  local(8)  delivery  agent
       should use for names that are not found in the aliases(5) or UNIX pass-
       word database.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

fallback_transport_maps (default: empty)
       Optional  lookup  tables with per-recipient message delivery transports
       for recipients that the local(8) delivery agent could not find  in  the
       aliases(5) or UNIX password database.

       The  precedence  of  local(8)  delivery  features  from high to low is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps,  mailbox_command, home_mailbox, mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       For safety reasons, this feature does not allow  $number  substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
       Optional  list  of  destinations  that are eligible for per-destination
       logfiles with mail that is queued to those destinations.

       By default, Postfix maintains "fast flush" logfiles only  for  destina-
       tions that the Postfix SMTP server is willing to relay to (i.e. the de-
       fault is: "fast_flush_domains = $relay_domains"; see the  relay_domains
       parameter in the postconf(5) manual).

       Specify  a list of hosts or domains, "/file/name" patterns or "type:ta-
       ble" lookup tables, separated by commas  and/or  whitespace.   Continue
       long  lines  by  starting the next line with whitespace. A "/file/name"
       pattern is replaced by its contents; a  "type:table"  lookup  table  is
       matched when the domain or its parent domain appears as lookup key.

       Pattern  matching  of domain names is controlled by the presence or ab-
       sence of "fast_flush_domains" in  the  parent_domain_matches_subdomains
       parameter value.

       Specify "fast_flush_domains =" (i.e., empty) to disable the feature al-
       together.

fast_flush_purge_time (default: 7d)
       The time after which an empty per-destination "fast flush"  logfile  is
       deleted.

       You can specify the time as a number, or as a number followed by a let-
       ter that  indicates  the  time  unit:  s=seconds,  m=minutes,  h=hours,
       d=days, w=weeks.  The default time unit is days.

fast_flush_refresh_time (default: 12h)
       The  time  after  which  a  non-empty  but unread per-destination "fast
       flush" logfile needs to be refreshed.  The contents of  a  logfile  are
       refreshed by requesting delivery of all messages listed in the logfile.

       You can specify the time as a number, or as a number followed by a let-
       ter that  indicates  the  time  unit:  s=seconds,  m=minutes,  h=hours,
       d=days, w=weeks.  The default time unit is hours.

fault_injection_code (default: 0)
       Force  specific  internal tests to fail, to test the handling of errors
       that are difficult to reproduce otherwise.

flush_service_name (default: flush)
       The name of the flush(8) service. This service  maintains  per-destina-
       tion  logfiles  with  the  queue  file names of mail that is queued for
       those destinations.

       This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
       The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
       The delay between attempts to fork() a child process.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)
       Restrict  the  characters  that  the  local(8) delivery agent allows in
       $name expansions of $forward_path.  Characters outside the allowed  set
       are replaced by underscores.

forward_path (default: see postconf -d output)
       The  local(8)  delivery  agent  search list for finding a .forward file
       with user-specified delivery methods. The first file that is  found  is
       used.

       The  forward_path value is not subject to Postfix configuration parame-
       ter $name expansion. Instead, the following $name expansions  are  done
       on  forward_path  before  the  search  actually happens.  The result of
       $name expansion is filtered with the character set  that  is  specified
       with the forward_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The  address extension delimiter that was found in the recipient
              address (Postfix 2.11 and later), or the  system-wide  recipient
              address extension delimiter (Postfix 2.10 and earlier).

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Examples:

       forward_path = /var/forward/$user
       forward_path =
           /var/forward/$user/.forward$recipient_delimiter$extension,
           /var/forward/$user/.forward

frozen_delivered_to (default: yes)
       Update  the local(8) delivery agent's idea of the Delivered-To: address
       (see prepend_delivered_header) only once, at the start  of  a  delivery
       attempt;  do  not  update  the  Delivered-To:  address  while expanding
       aliases or .forward files.

       This feature is available in Postfix 2.3 and later. With older  Postfix
       releases,  the behavior is as if this parameter is set to "no". The old
       setting can be expensive with deeply nested aliases or .forward  files.
       When  an  alias  or .forward file changes the Delivered-To: address, it
       ties up one queue file and one cleanup process instance while  mail  is
       being forwarded.

hash_queue_depth (default: 1)
       The number of subdirectory levels for queue directories listed with the
       hash_queue_names parameter. Queue hashing is  implemented  by  creating
       one  or  more  levels  of directories with one-character names.  Origi-
       nally, these directory names were equal to the first characters of  the
       queue  file  name, with the hexadecimal representation of the file cre-
       ation time in microseconds.

       With long queue file names, queue hashing produces the same results  as
       with  short  names. The file creation time in microseconds is converted
       into hexadecimal form before the result is used for queue hashing.  The
       base  16 encoding gives finer control over the number of subdirectories
       than is possible with the base 52 encoding of long queue file names.

       After changing the hash_queue_names or hash_queue_depth parameter, exe-
       cute the command "postfix reload".

hash_queue_names (default: deferred, defer)
       The names of queue directories that are split across multiple subdirec-
       tory levels.

       Before Postfix version 2.2, the default list of hashed queues was  sig-
       nificantly  larger. Claims about improvements in file system technology
       suggest that hashing of the incoming and active  queues  is  no  longer
       needed.  Fewer  hashed  directories speed up the time needed to restart
       Postfix.

       After changing the hash_queue_names or hash_queue_depth parameter, exe-
       cute the command "postfix reload".

header_address_token_limit (default: 10240)
       The  maximal number of address tokens are allowed in an address message
       header. Information that exceeds the limit is discarded.  The limit  is
       enforced by the cleanup(8) server.

header_checks (default: empty)
       Optional  lookup tables for content inspection of primary non-MIME mes-
       sage headers, as specified in the header_checks(5) manual page.

header_from_format (default: standard)
       The format of the Postfix-generated From: header. This setting  affects
       the  appearance of 'full name' information when a local program such as
       /bin/mail submits a message without From: header  through  the  Postfix
       sendmail(1) command.

       Specify one of the following:

       standard (default)
              Produce  a  header formatted as "From: name <address>".  This is
              the default as of Postfix 3.3.

       obsolete
              Produce a header formatted as "From: address  (name)".  This  is
              the behavior prior to Postfix 3.3.

       Notes:

       o      Postfix  generates the format "From: address" when name informa-
              tion is unavailable or the envelope  sender  address  is  empty.
              This is the same behavior as prior to Postfix 3.3.

       o      In  the  standard  form,  the name will be quoted if it contains
              specials as defined in RFC 5322, or the "!%" address operators.

       o      The Postfix sendmail(1) command gets name information  from  the
              -F  command-line  option, from the NAME environment variable, or
              from the UNIX password file.

       This feature is available in Postfix 3.3 and later.

header_size_limit (default: 102400)
       The maximal amount of memory in bytes for storing a message header.  If
       a  header is larger, the excess is discarded.  The limit is enforced by
       the cleanup(8) server.

helpful_warnings (default: yes)
       Log warnings about  problematic  configuration  settings,  and  provide
       helpful suggestions.

       This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
       Optional  pathname of a mailbox file relative to a local(8) user's home
       directory.

       Specify a pathname ending in "/" for qmail-style delivery.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Examples:

       home_mailbox = Mailbox
       home_mailbox = Maildir/

hopcount_limit (default: 50)
       The maximal number of Received:  message headers that is allowed in the
       primary message headers. A message that exceeds the limit  is  bounced,
       in order to stop a mailer loop.

html_directory (default: see postconf -d output)
       The  location of Postfix HTML files that describe how to build, config-
       ure or operate a specific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)
       Ignore DNS MX lookups that produce no response.  By default, the  Post-
       fix SMTP client defers delivery and tries again after some delay.  This
       behavior is required by the SMTP standard.

       Specify "ignore_mx_lookup_error = yes" to force a DNS A  record  lookup
       instead. This violates the SMTP standard and can result in mis-delivery
       of mail.

import_environment (default: see postconf -d output)
       The list of environment parameters that a  privileged  Postfix  process
       will  import  from a non-Postfix parent process, or name=value environ-
       ment overrides.  Unprivileged utilities  will  enforce  the  name=value
       overrides,  but  otherwise  will  not change their process environment.
       Examples of relevant parameters:

       TZ     May be needed for sane time keeping on  most  System-V-ish  sys-
              tems.

       DISPLAY
              Needed for debugging Postfix daemons with an X-windows debugger.

       XAUTHORITY
              Needed for debugging Postfix daemons with an X-windows debugger.

       MAIL_CONFIG
              Needed to make "postfix -c" work.

       Specify  a  list  of names and/or name=value pairs, separated by white-
       space or comma. Specify "{ name=value }" to protect whitespace or comma
       in  parameter  values  (whitespace after the opening "{" and before the
       closing "}" is ignored). The form name=value is supported with  Postfix
       version  2.1 and later; the use of {} is supported with Postfix 3.0 and
       later.

in_flow_delay (default: 1s)
       Time to pause before accepting a new message, when the message  arrival
       rate  exceeds  the  message delivery rate. This feature is turned on by
       default (it's disabled on SCO UNIX due to an SCO bug).

       With the default 100 Postfix SMTP server process limit,  "in_flow_delay
       =  1s" limits the mail inflow to 100 messages per second above the num-
       ber of messages delivered per second.

       Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
       The network interface addresses that this mail system receives mail on.
       Specify  "all" to receive mail on all network interfaces (default), and
       "loopback-only" to receive mail on  loopback  network  interfaces  only
       (Postfix  version 2.2 and later).  The parameter also controls delivery
       of mail to user@[ip.address].

       Note 1: you need to stop and start Postfix when this parameter changes.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

       When  inet_interfaces  specifies just one IPv4 and/or IPv6 address that
       is not a loopback address, the Postfix SMTP client will  use  this  ad-
       dress  as  the IP source address for outbound mail. Support for IPv6 is
       available in Postfix version 2.2 and later.

       On a multi-homed firewall with separate Postfix instances listening  on
       the  "inside"  and "outside" interfaces, this can prevent each instance
       from being able to reach remote SMTP servers on the "other side" of the
       firewall.  Setting  smtp_bind_address  to  0.0.0.0 avoids the potential
       problem for IPv4, and setting smtp_bind_address6 to :: solves the prob-
       lem for IPv6.

       A better solution for multi-homed firewalls is to leave inet_interfaces
       at the default value and instead use explicit IP addresses in the  mas-
       ter.cf  SMTP  server  definitions.   This  preserves  the  Postfix SMTP
       client's loop detection, by ensuring that each  side  of  the  firewall
       knows  that  the  other  IP  address  is  still  the same host. Setting
       $inet_interfaces to a single IPv4 and/or IPV6 address is primarily use-
       ful  with  virtual  hosting  of domains on secondary IP addresses, when
       each IP address serves a different domain (and has a different $myhost-
       name setting).

       See also the proxy_interfaces parameter, for network addresses that are
       forwarded to Postfix by way of a proxy or address translator.

       Examples:

       inet_interfaces = all (DEFAULT)
       inet_interfaces = loopback-only (Postfix version 2.2 and later)
       inet_interfaces = 127.0.0.1
       inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
       inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: all)
       The Internet protocols Postfix will attempt to use when making  or  ac-
       cepting connections. Specify one or more of "ipv4" or "ipv6", separated
       by whitespace or commas. The form "all" is equivalent to  "ipv4,  ipv6"
       or "ipv4", depending on whether the operating system implements IPv6.

       With  Postfix 2.8 and earlier the default is "ipv4". For backwards com-
       patibility with these releases, the Postfix 2.9 and later upgrade  pro-
       cedure  appends  an explicit "inet_protocols = ipv4" setting to main.cf
       when no explicit setting is present. This compatibility workaround will
       be phased out as IPv6 deployment becomes more common.

       This feature is available in Postfix 2.2 and later.

       Note: you MUST stop and start Postfix after changing this parameter.

       On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server
       will also accept IPv4 connections, even when IPv4 is  turned  off  with
       the  inet_protocols  parameter.   On  systems with IPV6_V6ONLY support,
       Postfix will use separate server sockets for IPv6 and  IPv4,  and  each
       will accept only connections for the corresponding protocol.

       When  IPv4 support is enabled via the inet_protocols parameter, Postfix
       will look up DNS type A records, and will convert  IPv4-in-IPv6  client
       IP  addresses  (::ffff:1.2.3.4)  to their original IPv4 form (1.2.3.4).
       The latter is needed on hosts that pre-date  IPV6_V6ONLY  support  (RFC
       3493).

       When  IPv6 support is enabled via the inet_protocols parameter, Postfix
       will do DNS type AAAA record lookups.

       When both IPv4 and IPv6 support are enabled, the  Postfix  SMTP  client
       will  choose the protocol as specified with the smtp_address_preference
       parameter. Postfix versions before 2.8 attempt to connect via IPv6  be-
       fore attempting to use IPv4.

       Examples:

       inet_protocols = ipv4
       inet_protocols = all (DEFAULT)
       inet_protocols = ipv6
       inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
       The  initial per-destination concurrency level for parallel delivery to
       the same destination.  With per-destination recipient limit > 1, a des-
       tination is a domain, otherwise it is a recipient.

       Use   transport_initial_destination_concurrency  to  specify  a  trans-
       port-specific override, where transport is the master.cf  name  of  the
       message delivery transport (Postfix 2.5 and later).

       Warning:  with concurrency of 1, one bad message can be enough to block
       all mail to a site.

internal_mail_filter_classes (default: empty)
       What categories of Postfix-generated mail are subject  to  before-queue
       content inspection by non_smtpd_milters, header_checks and body_checks.
       Specify zero or more of  the  following,  separated  by  whitespace  or
       comma.

       bounce Inspect the content of delivery status notifications.

       notify Inspect  the  content of postmaster notifications by the smtp(8)
              and smtpd(8) processes.

       NOTE: It's generally not safe to enable  content  inspection  of  Post-
       fix-generated email messages. The user is warned.

       This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
       The numerical Postfix SMTP server response code when the client HELO or
       EHLO command parameter is rejected by the  reject_invalid_helo_hostname
       restriction.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

ipc_idle (default: version dependent)
       The time after which a client closes  an  idle  internal  communication
       channel.  The purpose is to allow Postfix daemon processes to terminate
       voluntarily after they become idle. This is used, for example,  by  the
       Postfix address resolving and rewriting clients.

       With Postfix 2.4 the default value was reduced from 100s to 5s.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

ipc_timeout (default: 3600s)
       The time limit for sending or receiving information  over  an  internal
       communication  channel.  The purpose is to break out of deadlock situa-
       tions. If the time limit is exceeded the software aborts with  a  fatal
       error.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

ipc_ttl (default: 1000s)
       The time after which a client closes an active  internal  communication
       channel.  The purpose is to allow Postfix daemon processes to terminate
       voluntarily after reaching their client limit.  This is used, for exam-
       ple, by the Postfix address resolving and rewriting clients.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
       Upon input, long lines are chopped up  into  pieces  of  at  most  this
       length; upon delivery, long lines are reconstructed.

lmdb_map_size (default: 16777216)
       The  initial  OpenLDAP  LMDB database size limit in bytes.  Each time a
       database becomes full, its size limit is doubled.

       This feature is available in Postfix 2.11 and later.

lmtp_address_preference (default: ipv6)
       The LMTP-specific version of the smtp_address_preference  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_address_verify_target (default: rcpt)
       The  LMTP-specific version of the smtp_address_verify_target configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 3.0 and later.

lmtp_assume_final (default: no)
       When a remote LMTP server announces no DSN  support,  assume  that  the
       server  performs  final  delivery, and send "delivered" delivery status
       notifications instead of "relayed". The default  setting  is  backwards
       compatible  to avoid the infinitesimal possibility of breaking existing
       LMTP-based content filters.

lmtp_balance_inet_protocols (default: yes)
       The LMTP-specific version of the smtp_balance_inet_protocols configura-
       tion parameter. See there for details.

       This feature is available in Postfix 3.3 and later.

lmtp_bind_address (default: empty)
       The LMTP-specific version of the smtp_bind_address configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
       The LMTP-specific version of the smtp_bind_address6  configuration  pa-
       rameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)
       The LMTP-specific version of the smtp_body_checks configuration parame-
       ter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)
       Keep Postfix LMTP client connections open for up to $max_idle  seconds.
       When  the  LMTP  client  receives a request for the same connection the
       connection is reused.

       This parameter is available in Postfix version 2.2 and  earlier.   With
       Postfix  version  2.3  and  later, see lmtp_connection_cache_on_demand,
       lmtp_connection_cache_destinations,       or        lmtp_connection_re-
       use_time_limit.

       The  effectiveness of cached connections will be determined by the num-
       ber of remote LMTP servers in use, and the concurrency limit  specified
       for the Postfix LMTP client. Cached connections are closed under any of
       the following conditions:

       o      The Postfix LMTP client idle time limit is reached.  This  limit
              is specified with the Postfix max_idle configuration parameter.

       o      A  delivery  request  specifies a different destination than the
              one currently cached.

       o      The per-process limit on the  number  of  delivery  requests  is
              reached.   This limit is specified with the Postfix max_use con-
              figuration parameter.

       o      Upon the onset of another  delivery  request,  the  remote  LMTP
              server  associated  with the current session does not respond to
              the RSET command.

       Most of these limitations have been with the Postfix a connection cache
       that is shared among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
       The  LMTP-specific  version of the smtp_cname_overrides_servername con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
       The Postfix LMTP client time limit for completing a TCP connection,  or
       zero  (use  the operating system built-in time limit).  When no connec-
       tion can be made within the deadline, the LMTP client  tries  the  next
       address on the mail exchanger list.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       Example:

       lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
       The LMTP-specific  version  of  the  smtp_connection_cache_destinations
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
       The  LMTP-specific  version of the smtp_connection_cache_on_demand con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
       The LMTP-specific version of the smtp_connection_cache_time_limit  con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_count_limit (default: 0)
       The LMTP-specific version of the smtp_connection_reuse_count_limit con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_connection_reuse_time_limit (default: 300s)
       The LMTP-specific version of the smtp_connection_reuse_time_limit  con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
       The  Postfix  LMTP  client time limit for sending the LMTP ".", and for
       receiving the remote LMTP server response.  When  no  response  is  re-
       ceived  within  the  deadline, a warning is logged that the mail may be
       delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_data_init_timeout (default: 120s)
       The  Postfix  LMTP client time limit for sending the LMTP DATA command,
       and for receiving the remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)
       The  Postfix  LMTP  client time limit for sending the LMTP message con-
       tent.  When the connection stalls for more than $lmtp_data_xfer_timeout
       the LMTP client terminates the transfer.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)
       The LMTP-specific version of the smtp_defer_if_no_mx_address_found con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_delivery_status_filter (default: empty)
       The LMTP-specific version of the smtp_delivery_status_filter configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 3.0 and later.

lmtp_destination_concurrency_limit   (default:    $default_destination_concur-
       rency_limit)
       The  maximal  number of parallel deliveries to the same destination via
       the lmtp message delivery transport. This  limit  is  enforced  by  the
       queue  manager.  The message delivery transport name is the first field
       in the entry in the master.cf file.

lmtp_destination_recipient_limit    (default:     $default_destination_recipi-
       ent_limit)
       The  maximal  number of recipients per message for the lmtp message de-
       livery transport. This limit is enforced by the queue manager. The mes-
       sage  delivery  transport  name  is the first field in the entry in the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of lmtp_des-
       tination_concurrency_limit from concurrency per domain into concurrency
       per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote LMTP server address, with case in-
       sensitive  lists  of  LHLO  keywords (pipelining, starttls, auth, etc.)
       that the Postfix LMTP client will ignore in the LHLO  response  from  a
       remote LMTP server. See lmtp_discard_lhlo_keywords for details. The ta-
       ble  is  not  indexed  by  hostname  for  consistency  with  smtpd_dis-
       card_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
       A  case  insensitive list of LHLO keywords (pipelining, starttls, auth,
       etc.) that the Postfix LMTP client will ignore  in  the  LHLO  response
       from a remote LMTP server.

       This feature is available in Postfix 2.3 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

       o      Use the lmtp_discard_lhlo_keyword_address_maps feature  to  dis-
              card LHLO keywords selectively.

lmtp_dns_reply_filter (default: empty)
       Optional  filter  for  Postfix  LMTP  client  DNS  lookup results.  See
       smtp_dns_reply_filter for details including an example.

       This feature is available in Postfix 3.0 and later.

lmtp_dns_resolver_options (default: empty)
       The LMTP-specific version of the  smtp_dns_resolver_options  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_dns_support_level (default: empty)
       The  LMTP-specific  version of the smtp_dns_support_level configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_enforce_tls (default: no)
       The LMTP-specific version of the smtp_enforce_tls configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_fallback_relay (default: empty)
       Optional  list of relay hosts for LMTP destinations that can't be found
       or that are unreachable.  In main.cf elements are separated  by  white-
       space or commas.

       By  default,  mail  is returned to the sender when a destination is not
       found, and delivery is deferred when a destination is unreachable.

       The fallback relays must be TCP destinations, specified without a lead-
       ing  "inet:" prefix.  Specify a host or host:port.  Since MX lookups do
       not apply  with  LMTP,  there  is  no  need  to  use  the  "[host]"  or
       "[host]:port"  forms.  If you specify multiple LMTP destinations, Post-
       fix will try them in the specified order.

       This feature is available in Postfix 3.1 and later.

lmtp_generic_maps (default: empty)
       The LMTP-specific version of the smtp_generic_maps configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)
       The  LMTP-specific  version of the smtp_header_checks configuration pa-
       rameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)
       The LMTP-specific version of the smtp_host_lookup configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
       The hostname to send in the LMTP LHLO command.

       The  default  value  is  the  machine  hostname.  Specify a hostname or
       [ip.add.re.ss].

       This information can be specified in the  main.cf  file  for  all  LMTP
       clients,  or  it  can be specified in the master.cf file for a specific
       client, for example:

           /etc/postfix/master.cf:
               mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the  LHLO  command,  and
       for receiving the initial remote LMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_line_length_limit (default: 990)
       The LMTP-specific version of the  smtp_line_length_limit  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
       The  Postfix  LMTP client time limit for sending the MAIL FROM command,
       and for receiving the remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_mime_header_checks (default: empty)
       The  LMTP-specific version of the smtp_mime_header_checks configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)
       The LMTP-specific version of  the  smtp_mx_address_limit  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
       The  LMTP-specific  version  of the smtp_mx_session_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)
       The LMTP-specific version of the  smtp_nested_header_checks  configura-
       tion parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_per_record_deadline (default: no)
       The LMTP-specific version of the smtp_per_record_deadline configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_pix_workaround_delay_time (default: 10s)
       The LMTP-specific version of the smtp_pix_workaround_delay_time config-
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
       The LMTP-specific version of the smtp_pix_workaround_maps configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
       The LMTP-specific  version  of  the  smtp_pix_workaround_threshold_time
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
       The  LMTP-specific version of the smtp_pix_workaround configuration pa-
       rameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the  QUIT  command,  and
       for receiving the remote LMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)
       The LMTP-specific version of the smtp_quote_rfc821_envelope  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
       The LMTP-specific version of the smtp_randomize_addresses configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the RCPT TO command, and
       for receiving the remote LMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_reply_filter (default: empty)
       The LMTP-specific version of the smtp_reply_filter configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)
       The  Postfix  LMTP  client time limit for sending the RSET command, and
       for receiving the remote LMTP server response. The  LMTP  client  sends
       RSET  in order to finish a recipient address probe, or to verify that a
       cached connection is still alive.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)
       The  LMTP-specific  version of the smtp_sasl_auth_cache_name configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)
       The LMTP-specific version of the  smtp_sasl_auth_cache_time  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)
       The  LMTP-specific version of the smtp_sasl_auth_soft_bounce configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)
       The LMTP-specific version of the smtp_sasl_mechanism_filter  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
       Optional  Postfix  LMTP client lookup tables with one username:password
       entry per host or domain.  If a remote host  or  domain  has  no  user-
       name:password  entry,  then the Postfix LMTP client will not attempt to
       authenticate to the remote host.

lmtp_sasl_path (default: empty)
       Implementation-specific information that is passed through to the  SASL
       plug-in implementation that is selected with lmtp_sasl_type.  Typically
       this specifies the name of a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
       SASL security options; as of Postfix 2.3 the list of available features
       depends  on  the  SASL  client  implementation  that  is  selected with
       lmtp_sasl_type.

       The following security features are defined for the cyrus  client  SASL
       implementation:

       noplaintext
              Disallow authentication methods that use plaintext passwords.

       noactive
              Disallow  authentication methods that are vulnerable to non-dic-
              tionary active attacks.

       nodictionary
              Disallow authentication methods that are vulnerable  to  passive
              dictionary attack.

       noanonymous
              Disallow anonymous logins.

       Example:

       lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
       The LMTP-specific version of the smtp_sasl_tls_security_options config-
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options (default:  $lmtp_sasl_tls_security_op-
       tions)
       The  LMTP-specific  version  of the smtp_sasl_tls_verified_security_op-
       tions configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
       The SASL plug-in type that the Postfix LMTP client should use  for  au-
       thentication.   The  available  types are listed with the "postconf -A"
       command.

       This feature is available in Postfix 2.3 and later.

lmtp_send_dummy_mail_auth (default: no)
       The LMTP-specific version of the  smtp_send_dummy_mail_auth  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_send_xforward_command (default: no)
       Send  an  XFORWARD command to the remote LMTP server when the LMTP LHLO
       server response announces XFORWARD support.  This allows an lmtp(8) de-
       livery agent, used for content filter message injection, to forward the
       name, address, protocol and HELO name of the  original  client  to  the
       content  filter  and downstream queuing LMTP server.  Before you change
       the value to yes, it is best to make sure that your content filter sup-
       ports this command.

       This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
       The  LMTP-specific  version of the smtp_sender_dependent_authentication
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
       The LMTP-specific version of the  smtp_skip_5xx_greeting  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
       Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
       The  LMTP-specific  version  of the smtp_starttls_timeout configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
       The default TCP port that the Postfix LMTP client connects to.  Specify
       a symbolic name (see services(5)) or a numeric port.

lmtp_tls_CAfile (default: empty)
       The  LMTP-specific version of the smtp_tls_CAfile configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
       The LMTP-specific version of the smtp_tls_CApath configuration  parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)
       The  LMTP-specific  version of the smtp_tls_block_early_mail_reply con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)
       The LMTP-specific version of the smtp_tls_cert_file  configuration  pa-
       rameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_chain_files (default: empty)
       The LMTP-specific version of the smtp_tls_chain_files configuration pa-
       rameter. See there for details.

       This feature is available in Postfix 3.4 and later.

lmtp_tls_ciphers (default: medium)
       The LMTP-specific version of the smtp_tls_ciphers configuration parame-
       ter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_connection_reuse (default: no)
       The  LMTP-specific  version of the smtp_tls_connection_reuse configura-
       tion parameter. See there for details.

       This feature is available in Postfix 3.4 and later.

lmtp_tls_dcert_file (default: empty)
       The LMTP-specific version of the smtp_tls_dcert_file configuration  pa-
       rameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
       The  LMTP-specific  version of the smtp_tls_dkey_file configuration pa-
       rameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)
       The LMTP-specific version of the smtp_tls_eccert_file configuration pa-
       rameter.  See there for details.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)
       The LMTP-specific version of the smtp_tls_eckey_file configuration  pa-
       rameter.  See there for details.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)
       The LMTP-specific version of the  smtp_tls_enforce_peername  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_exclude_ciphers configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)
       The LMTP-specific version of the  smtp_tls_fingerprint_cert_match  con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)
       The LMTP-specific version of the smtp_tls_fingerprint_digest configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_force_insecure_host_tlsa_lookup (default: no)
       The    LMTP-specific    version     of     the     smtp_tls_force_inse-
       cure_host_tlsa_lookup configuration parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
       The LMTP-specific version of the smtp_tls_key_file configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
       The LMTP-specific version of the smtp_tls_loglevel configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: medium)
       The  LMTP-specific version of the smtp_tls_mandatory_ciphers configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
       The LMTP-specific  version  of  the  smtp_tls_mandatory_exclude_ciphers
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3)
       The  LMTP-specific version of the smtp_tls_mandatory_protocols configu-
       ration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
       The LMTP-specific version of the smtp_tls_note_starttls_offer  configu-
       ration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
       The LMTP-specific version of the smtp_tls_per_site configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
       The LMTP-specific version of the smtp_tls_policy_maps configuration pa-
       rameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: !SSLv2, !SSLv3)
       The  LMTP-specific  version of the smtp_tls_protocols configuration pa-
       rameter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)
       The LMTP-specific version of the smtp_tls_scert_verifydepth  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
       The  LMTP-specific version of the smtp_tls_secure_cert_match configura-
       tion parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)
       The LMTP-specific version of the smtp_tls_security_level  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_servername (default: empty)
       The  LMTP-specific version of the smtp_tls_servername configuration pa-
       rameter. See there for details.

       This feature is available in Postfix 3.4 and later.

lmtp_tls_session_cache_database (default: empty)
       The LMTP-specific version of the  smtp_tls_session_cache_database  con-
       figuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
       The LMTP-specific version of the smtp_tls_session_cache_timeout config-
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_trust_anchor_file (default: empty)
       The LMTP-specific version of the smtp_tls_trust_anchor_file  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_tls_verify_cert_match (default: hostname)
       The  LMTP-specific version of the smtp_tls_verify_cert_match configura-
       tion parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
       The LMTP-specific version of the smtp_use_tls configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
       The  Postfix  LMTP  client time limit for sending the XFORWARD command,
       and for receiving the remote LMTP server response.

       In case of problems the client does NOT try the  next  address  on  the
       mail exchanger list.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
       Optional shell program for local(8) delivery  to  non-Postfix  command.
       By  default,  non-Postfix  commands are executed directly; commands are
       given to given to the default shell (typically, /bin/sh) only when they
       contain shell meta characters or shell built-in commands.

       "sendmail's  restricted  shell" (smrsh) is what most people will use in
       order to restrict what programs can be run  from  e.g.  .forward  files
       (smrsh is part of the Sendmail distribution).

       Note:  when  a  shell program is specified, it is invoked even when the
       command contains no shell built-in commands or meta characters.

       Example:

       local_command_shell = /some/where/smrsh -c
       local_command_shell = /bin/bash -c

local_delivery_status_filter (default: $default_delivery_status_filter)
       Optional filter for the local(8) delivery agent to  change  the  status
       code or explanatory text of successful or unsuccessful deliveries.  See
       default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

local_destination_concurrency_limit (default: 2)
       The maximal number of parallel deliveries via the local  mail  delivery
       transport   to  the  same  recipient  (when  "local_destination_recipi-
       ent_limit = 1") or the maximal number of  parallel  deliveries  to  the
       same  local domain (when "local_destination_recipient_limit > 1"). This
       limit is enforced by the queue manager. The message delivery  transport
       name is the first field in the entry in the master.cf file.

       A  low limit of 2 is recommended, just in case someone has an expensive
       shell command in a .forward file or in an alias (e.g., a  mailing  list
       manager).  You don't want to run lots of those at the same time.

local_destination_recipient_limit (default: 1)
       The  maximal  number  of  recipients per message delivery via the local
       mail delivery transport. This limit is enforced by the  queue  manager.
       The  message delivery transport name is the first field in the entry in
       the master.cf file.

       Setting this parameter to a value > 1 changes the meaning of local_des-
       tination_concurrency_limit  from concurrency per recipient into concur-
       rency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
       Rewrite message header addresses in mail from these clients and  update
       incomplete  addresses  with  the domain name in $myorigin or $mydomain;
       either don't rewrite message headers from other clients at all, or  re-
       write  message  headers and update incomplete addresses with the domain
       specified in the remote_header_rewrite_domain parameter.

       See the append_at_myorigin and append_dot_mydomain parameters  for  de-
       tails of how domain names are appended to incomplete addresses.

       Specify a list of zero or more of the following:

       permit_inet_interfaces
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches $inet_interfaces. This is enabled by default.

       permit_mynetworks
              Append the domain name in $myorigin or $mydomain when the client
              IP  address  matches  any  network  or network address listed in
              $mynetworks. This setting will not prevent  remote  mail  header
              address rewriting when mail from a remote client is forwarded by
              a neighboring system.

       permit_sasl_authenticated
              Append the domain name in $myorigin or $mydomain when the client
              is successfully authenticated via the RFC 4954 (AUTH) protocol.

       permit_tls_clientcerts
              Append the domain name in $myorigin or $mydomain when the remote
              SMTP client TLS certificate fingerprint or  public  key  finger-
              print  (Postfix  2.9 and later) is listed in $relay_clientcerts.
              The  fingerprint  digest  algorithm  is  configurable  via   the
              smtpd_tls_fingerprint_digest  parameter (hard-coded as md5 prior
              to Postfix version 2.5).

       permit_tls_all_clientcerts
              Append the domain name in $myorigin or $mydomain when the remote
              SMTP client TLS certificate is successfully verified, regardless
              of whether it is listed on the server,  and  regardless  of  the
              certifying authority.

       check_address_map type:table

       type:table
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches the specified lookup table.  The  lookup  re-
              sult  is ignored, and no subnet lookup is done. This is suitable
              for, e.g., pop-before-smtp lookup tables.

       Examples:

       The Postfix < 2.2 backwards compatible setting: always rewrite  message
       headers,  and  always  append  my  own  domain to incomplete header ad-
       dresses.

           local_header_rewrite_clients = static:all

       The purist (and default) setting: rewrite headers  only  in  mail  from
       Postfix sendmail and in SMTP mail from this machine.

           local_header_rewrite_clients = permit_inet_interfaces

       The intermediate setting: rewrite header addresses and append $myorigin
       or $mydomain information only with mail from Postfix sendmail, from lo-
       cal clients, or from authorized SMTP clients.

       Note:  this setting will not prevent remote mail header address rewrit-
       ing when mail from a remote client is forwarded by a  neighboring  sys-
       tem.

           local_header_rewrite_clients = permit_mynetworks,
               permit_sasl_authenticated permit_tls_clientcerts
               check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
       Lookup tables with all names or addresses of local recipients: a recip-
       ient address is local when its domain matches $mydestination, $inet_in-
       terfaces  or $proxy_interfaces.  Specify @domain as a wild-card for do-
       mains that do not have a valid  recipient  list.   Technically,  tables
       listed  with  $local_recipient_maps are used as lists: Postfix needs to
       know only if a lookup string is found or not, but it does not  use  the
       result from table lookup.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       If  this  parameter  is  non-empty (the default), then the Postfix SMTP
       server will reject mail for unknown local users.

       To turn off local recipient checking in the Postfix SMTP server,  spec-
       ify "local_recipient_maps =" (i.e. empty).

       The  default setting assumes that you use the default Postfix local de-
       livery agent for local delivery. You need to update  the  local_recipi-
       ent_maps setting if:

       o      You redefine the local delivery agent in master.cf.

       o      You redefine the "local_transport" setting in main.cf.

       o      You   use  the  "luser_relay",  "mailbox_transport",  or  "fall-
              back_transport" feature of the Postfix local(8) delivery agent.

       Details are described in the LOCAL_RECIPIENT_README file.

       Beware: if the Postfix SMTP server runs chrooted, you  need  to  access
       the  passwd  file via the proxymap(8) service, in order to overcome ch-
       root access restrictions. The alternative, maintaining a  copy  of  the
       system password file in the chroot jail is not practical.

       Examples:

       local_recipient_maps =

local_transport (default: local:$myhostname)
       The  default mail delivery transport and next-hop destination for final
       delivery to domains listed with mydestination, and for [ipaddress] des-
       tinations  that  match $inet_interfaces or $proxy_interfaces.  This in-
       formation can be overruled with the transport(5) table.

       By default, local mail is delivered to the  transport  called  "local",
       which is just the name of a service that is defined the master.cf file.

       Specify  a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.   The  :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Beware: if you override the default local delivery agent then you  need
       to  review  the  LOCAL_RECIPIENT_README  document,  otherwise  the SMTP
       server may reject mail for local recipients.

luser_relay (default: empty)
       Optional catch-all destination for unknown local(8) recipients.  By de-
       fault,  mail  for  unknown recipients in domains that match $mydestina-
       tion, $inet_interfaces or $proxy_interfaces is returned  as  undeliver-
       able.

       The luser_relay value is not subject to Postfix configuration parameter
       $name expansion. Instead, the following $name expansions are done:

       $domain
              The recipient domain.

       $extension
              The recipient address extension.

       $home  The recipient's home directory.

       $local The entire recipient address localpart.

       $recipient
              The full recipient address.

       $recipient_delimiter
              The address extension delimiter that was found in the  recipient
              address  (Postfix  2.11 and later), or the system-wide recipient
              address extension delimiter (Postfix 2.10 and earlier).

       $shell The recipient's login shell.

       $user  The recipient username.

       ${name?value}
              Expands to value when $name has a non-empty value.

       ${name:value}
              Expands to value when $name has an empty value.

       Instead of $name you can also specify ${name} or $(name).

       Note: luser_relay works only for the Postfix local(8) delivery agent.

       Note: if you use this feature for accounts not  in  the  UNIX  password
       file,  then  you  must specify "local_recipient_maps =" (i.e. empty) in
       the main.cf file, otherwise the Postfix SMTP server  will  reject  mail
       for non-UNIX accounts with "User unknown in local recipient table".

       Examples:

       luser_relay = $user@other.host
       luser_relay = $local@other.host
       luser_relay = admin+$local

mail_name (default: Postfix)
       The  mail  system  name  that is displayed in Received: headers, in the
       SMTP greeting banner, and in bounced mail.

mail_owner (default: postfix)
       The UNIX system account that owns the Postfix queue  and  most  Postfix
       daemon  processes.   Specify  the  name of an unprivileged user account
       that does not share a user or group ID with other  accounts,  and  that
       owns  no  other files or processes on the system.  In particular, don't
       specify nobody or daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.

       When this parameter value  is  changed  you  need  to  re-run  "postfix
       set-permissions"  (with  Postfix  version  2.0 and earlier: "/etc/post-
       fix/post-install set-permissions".

mail_release_date (default: see postconf -d output)
       The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
       The directory where local(8) UNIX-style mailboxes are kept. The default
       setting  depends  on  the  system  type. Specify a name ending in / for
       maildir-style delivery.

       Note: maildir delivery is done with the privileges  of  the  recipient.
       If you use the mail_spool_directory setting for maildir style delivery,
       then you must create the top-level maildir directory in advance.  Post-
       fix will not create it.

       Examples:

       mail_spool_directory = /var/mail
       mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
       The  version  of  the  mail system. Stable releases are named major.mi-
       nor.patchlevel. Experimental releases also include  the  release  date.
       The  version string can be used in, for example, the SMTP greeting ban-
       ner.

mailbox_command (default: empty)
       Optional external command that the local(8) delivery agent  should  use
       for mailbox delivery.  The command is run with the user ID and the pri-
       mary group ID privileges of the recipient.  Exception: command delivery
       for  root executes with $default_privs privileges.  This is not a prob-
       lem, because 1) mail for root should always be aliased to a  real  user
       and 2) don't log in as root, use "su" instead.

       The following environment variables are exported to the command:

       CLIENT_ADDRESS
              Remote  client network address. Available in Postfix version 2.2
              and later.

       CLIENT_HELO
              Remote client EHLO command parameter. Available in Postfix  ver-
              sion 2.2 and later.

       CLIENT_HOSTNAME
              Remote  client  hostname.  Available  in Postfix version 2.2 and
              later.

       CLIENT_PROTOCOL
              Remote client protocol. Available in  Postfix  version  2.2  and
              later.

       DOMAIN The domain part of the recipient address.

       EXTENSION
              The optional address extension.

       HOME   The recipient home directory.

       LOCAL  The recipient address localpart.

       LOGNAME
              The recipient's username.

       ORIGINAL_RECIPIENT
              The  entire  recipient  address, before any address rewriting or
              aliasing.

       RECIPIENT
              The full recipient address.

       SASL_METHOD
              SASL authentication method specified in the remote  client  AUTH
              command. Available in Postfix version 2.2 and later.

       SASL_SENDER
              SASL  sender  address  specified  in the remote client MAIL FROM
              command. Available in Postfix version 2.2 and later.

       SASL_USER
              SASL username specified  in  the  remote  client  AUTH  command.
              Available in Postfix version 2.2 and later.

       SENDER The full sender address.

       SHELL  The recipient's login shell.

       USER   The recipient username.

       Unlike  other Postfix configuration parameters, the mailbox_command pa-
       rameter is not subjected to $name substitutions. This  is  to  make  it
       easier to specify shell syntax (see example below).

       If you can, avoid shell meta characters because they will force Postfix
       to run an expensive shell process. If you're delivering via  "procmail"
       then  running  a  shell won't make a noticeable difference in the total
       cost.

       Note: if you use the  mailbox_command  feature  to  deliver  mail  sys-
       tem-wide,  you  must  set  up an alias that forwards mail for root to a
       real user.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Examples:

       mailbox_command = /some/where/procmail
       mailbox_command = /some/where/procmail -a "$EXTENSION"
       mailbox_command = /some/where/maildrop -d "$USER"
               -f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
       Optional  lookup tables with per-recipient external commands to use for
       local(8) mailbox delivery.  Behavior is as with mailbox_command.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

mailbox_delivery_lock (default: see postconf -d output)
       How  to  lock a UNIX-style local(8) mailbox before attempting delivery.
       For a list of available file locking methods,  use  the  "postconf  -l"
       command.

       This  setting  is ignored with maildir style delivery, because such de-
       liveries are safe without explicit locks.

       Note: The dotlock method requires that the recipient  UID  or  GID  has
       write access to the parent directory of the mailbox file.

       Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
       The maximal size of any local(8) individual mailbox or maildir file, or
       zero (no limit).  In fact, this limits the size of  any  file  that  is
       written  to  upon  local  delivery, including files written by external
       commands that are executed by the local(8) delivery agent.

       This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
       Optional message delivery transport that the  local(8)  delivery  agent
       should use for mailbox delivery to all local recipients, whether or not
       they are found in the UNIX passwd database.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

mailbox_transport_maps (default: empty)
       Optional  lookup  tables with per-recipient message delivery transports
       to use for local(8) mailbox delivery, whether or not the recipients are
       found in the UNIX passwd database.

       The  precedence  of  local(8)  delivery  features  from high to low is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps,  mailbox_command, home_mailbox, mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       For safety reasons, this feature does not allow  $number  substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

maillog_file (default: empty)
       The  name  of  an optional logfile that is written by the Postfix post-
       logd(8) service. An empty value selects logging to syslogd(8).  Specify
       "/dev/stdout"  to select logging to standard output. Stdout logging re-
       quires that Postfix is started with "postfix start-fg".

       Note 1: The maillog_file parameter value must contain a prefix that  is
       specified with the maillog_file_prefixes parameter.

       Note  2:  Some Postfix non-daemon programs may still log information to
       syslogd(8), before they have processed their  configuration  parameters
       and command-line options.

       This feature is available in Postfix 3.4 and later.

maillog_file_compressor (default: gzip)
       The  program  to  run after rotating $maillog_file with "postfix logro-
       tate". The command is run with the rotated logfile name  as  its  first
       argument.

       This feature is available in Postfix 3.4 and later.

maillog_file_prefixes (default: /var, /dev/stdout)
       A  list  of allowed prefixes for a maillog_file value. This is a safety
       feature to contain the damage  from  a  single  configuration  mistake.
       Specify one or more prefix strings, separated by comma or whitespace.

       This feature is available in Postfix 3.4 and later.

maillog_file_rotate_suffix (default: %Y%m%d-%H%M%S)
       The  format of the suffix to append to $maillog_file while rotating the
       file with "postfix logrotate". See strftime(3) for syntax. The  default
       suffix, YYYYMMDD-HHMMSS, allows logs to be rotated frequently.

       This feature is available in Postfix 3.4 and later.

mailq_path (default: see postconf -d output)
       Sendmail   compatibility  feature  that  specifies  where  the  Postfix
       mailq(1) command is installed. This command can be  used  to  list  the
       Postfix mail queue.

manpage_directory (default: see postconf -d output)
       Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
       Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
       The  numerical  Postfix  SMTP  server  response code when a remote SMTP
       client   request   is   blocked   by   the    reject_rbl_client,    re-
       ject_rhsbl_client,  reject_rhsbl_reverse_client, reject_rhsbl_sender or
       reject_rhsbl_recipient restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)

       What addresses are subject to address masquerading.

       By default, address masquerading is  limited  to  envelope  sender  ad-
       dresses, and to header sender and header recipient addresses.  This al-
       lows you to use address masquerading on a mail gateway while still  be-
       ing able to forward mail to users on individual machines.

       Specify   zero   or   more   of:  envelope_sender,  envelope_recipient,
       header_sender, header_recipient

masquerade_domains (default: empty)
       Optional list of domains whose subdomain structure will be stripped off
       in email addresses.

       The  list is processed left to right, and processing stops at the first
       match.  Thus,

           masquerade_domains = foo.example.com example.com

       strips "user@any.thing.foo.example.com" to "user@foo.example.com",  but
       strips "user@any.thing.else.example.com" to "user@example.com".

       A  domain  name  prefixed with ! means do not masquerade this domain or
       its subdomains. Thus,

           masquerade_domains = !foo.example.com example.com

       does not  change  "user@any.thing.foo.example.com"  or  "user@foo.exam-
       ple.com",  but  strips "user@any.thing.else.example.com" to "user@exam-
       ple.com".

       Note: with Postfix version 2.2,  message  header  address  masquerading
       happens only when message header address rewriting is enabled:

       o      The message is received with the Postfix sendmail(1) command,

       o      The  message is received from a network client that matches $lo-
              cal_header_rewrite_clients,

       o      The  message  is  received  from  the  network,  and   the   re-
              mote_header_rewrite_domain   parameter   specifies  a  non-empty
              value.

       To  get  the  behavior  before  Postfix  version  2.2,   specify   "lo-
       cal_header_rewrite_clients = static:all".

       Example:

       masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
       Optional  list  of  user  names  that are not subjected to address mas-
       querading, even when their addresses match $masquerade_domains.

       By default, address masquerading makes no exceptions.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by  its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).   Con-
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a name from the list. The form  "!/file/name"  is
       supported only in Postfix version 2.4 and later.

       Examples:

       masquerade_exceptions = root, mailer-daemon
       masquerade_exceptions = root

master_service_disable (default: empty)
       Selectively disable master(8) listener ports by service type or by ser-
       vice name and type.  Specify a list of service types  ("inet",  "unix",
       "fifo",  or  "pass")  or  "name/type" tuples, where "name" is the first
       field of a master.cf entry and "type" is a service type. As with  other
       Postfix  matchlists, a search stops at the first match.  Specify "!pat-
       tern" to exclude a service from the list.  By  default,  all  master(8)
       listener ports are enabled.

       Note:  this  feature does not support "/file/name" or "type:table" pat-
       terns, nor does it support wildcards such as "*" or "all". This is  in-
       tentional.

       Examples:

       # With Postfix 2.6..2.10 use '.' instead of '/'.
       # Turn on all master(8) listener ports (the default).
       master_service_disable =
       # Turn off only the main SMTP listener port.
       master_service_disable = smtp/inet
       # Turn off all TCP/IP listener ports.
       master_service_disable = inet
       # Turn off all TCP/IP listener ports except "foo".
       master_service_disable = !foo/inet, inet

       This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)
       The  maximum  amount  of time that an idle Postfix daemon process waits
       for an incoming connection before terminating voluntarily.  This param-
       eter  is  ignored  by the Postfix queue manager and by other long-lived
       Postfix daemon processes.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

max_use (default: 100)
       The  maximal  number  of  incoming  connections  that  a Postfix daemon
       process will service before terminating voluntarily.  This parameter is
       ignored  by  the  Postfix queue manager and by other long-lived Postfix
       daemon processes.

maximal_backoff_time (default: 4000s)
       The maximal time between attempts to deliver a deferred message.

       This parameter should be set to a value greater than or equal to $mini-
       mal_backoff_time. See also $queue_run_delay.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

maximal_queue_lifetime (default: 5d)
       Consider a message as undeliverable, when delivery fails with a  tempo-
       rary   error,  and  the  time  in  the  queue  has  reached  the  maxi-
       mal_queue_lifetime limit.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

message_drop_headers (default: bcc, content-length, resent-bcc, return-path)
       Names  of  message headers that the cleanup(8) daemon will remove after
       applying header_checks(5) and before invoking Milter applications.  The
       default setting is compatible with Postfix < 3.0.

       Specify a list of header names, separated by comma or space.  Names are
       matched in a case-insensitive manner.  The  list  of  supported  header
       names is limited only by available memory.

       This feature is available in Postfix 3.0 and later.

message_reject_characters (default: empty)
       The set of characters that Postfix will reject in message content.  The
       usual C-like escape sequences are recognized: \a \b \f \n \r \t \v \ddd
       (up to three octal digits) and \\.

       Note  1: this feature does not recognize text that requires MIME decod-
       ing. It inspects raw  message  content,  just  like  header_checks  and
       body_checks.

       Note  2:  this  feature  is  disabled  with "receive_override_options =
       no_header_body_checks".

       Example:

       message_reject_characters = \0

       This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
       The maximal size in bytes of a message, including envelope information.

       Note: be careful when making changes.  Excessively  small  values  will
       result in the loss of non-delivery notifications, when a bounce message
       size exceeds the local or remote MTA's message size limit.

message_strip_characters (default: empty)
       The set of characters that Postfix will remove  from  message  content.
       The  usual C-like escape sequences are recognized: \a \b \f \n \r \t \v
       \ddd (up to three octal digits) and \\.

       Note 1: this feature does not recognize text that requires MIME  decod-
       ing.  It  inspects  raw  message  content,  just like header_checks and
       body_checks.

       Note 2: this  feature  is  disabled  with  "receive_override_options  =
       no_header_body_checks".

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 and later.

meta_directory (default: see 'postconf -d' output)
       The  location  of  non-executable  files that are shared among multiple
       Postfix instances,  such  as  postfix-files,  dynamicmaps.cf,  and  the
       multi-instance  template files main.cf.proto and master.cf.proto.  This
       directory should contain only Postfix-related  files.   Typically,  the
       meta_directory  parameter  has the same default as the config_directory
       parameter (/etc/postfix or /usr/local/etc/postfix).

       For backwards compatibility with Postfix  versions  2.6..2.11,  specify
       "meta_directory  =  $daemon_directory"  in main.cf before installing or
       upgrading Postfix, or specify  "meta_directory  =  /path/name"  on  the
       "make makefiles", "make install" or "make upgrade" command line.

       This feature is available in Postfix 3.0 and later.

milter_command_timeout (default: 30s)
       The  time  limit  for sending an SMTP command to a Milter (mail filter)
       application, and for receiving the response.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)
       The macros that are sent to Milter  (mail  filter)  applications  after
       completion  of  an  SMTP  connection.  See  MILTER_README for a list of
       available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
       The time limit for connecting to a Milter  (mail  filter)  application,
       and for negotiating protocol options.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
       The  time  limit  for sending message content to a Milter (mail filter)
       application, and for receiving the response.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)
       The macros that are sent to version 4 or higher  Milter  (mail  filter)
       applications  after the SMTP DATA command. See MILTER_README for a list
       of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
       The default action when a Milter (mail filter) application is  unavail-
       able or mis-configured. Specify one of the following:

       accept Proceed as if the mail filter was not present.

       reject Reject  all  further  commands  in this session with a permanent
              status code.

       tempfail
              Reject all further commands in this  session  with  a  temporary
              status code.

       quarantine
              Like  "accept",  but  freeze  the  message  in the "hold" queue.
              Available with Postfix 2.6 and later.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       message  end-of-data.  See  MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       end  of  the  message header. See MILTER_README for a list of available
       macro names and their meanings.

       This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)
       Optional lookup tables for content inspection of message  headers  that
       are  produced  by Milter applications.  See the header_checks(5) manual
       page available actions. Currently, PREPEND is not implemented.

       The following example sends all mail that is marked as SPAM to  a  spam
       handling machine. Note that matches are case-insensitive by default.

       /etc/postfix/main.cf:
           milter_header_checks = pcre:/etc/postfix/milter_header_checks

       /etc/postfix/milter_header_checks:
           /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

       The milter_header_checks mechanism could also be used for whitelisting.
       For example it could be used  to  skip  heavy  content  inspection  for
       DKIM-signed mail from known friendly domains.

       This  feature is available in Postfix 2.7, and as an optional patch for
       Postfix 2.6.

milter_helo_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP  HELO  or  EHLO command. See MILTER_README for a list of available
       macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
       The {daemon_name} macro value for Milter  (mail  filter)  applications.
       See  MILTER_README  for a list of available macro names and their mean-
       ings.

       This feature is available in Postfix 2.3 and later.

milter_macro_defaults (default: empty)
       Optional list of name=value pairs that specify default values for arbi-
       trary  macros  that Postfix may send to Milter applications.  These de-
       faults are used when there is no  corresponding  information  from  the
       message delivery context.

       Specify  name=value  or {name}=value pairs separated by comma or white-
       space.  Enclose a pair in "{}" when a value contains  comma  or  white-
       space (this form ignores whitespace after the enclosing "{", around the
       "=", and before the enclosing "}").

       This feature is available in Postfix 3.1 and later.

milter_macro_v (default: $mail_name $mail_version)
       The {v} macro value for Milter (mail filter)  applications.   See  MIL-
       TER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP MAIL FROM command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)
       The  mail  filter protocol version and optional protocol extensions for
       communication with a Milter application; prior to Postfix 2.6  the  de-
       fault  protocol is 2. Postfix sends this version number during the ini-
       tial protocol handshake.  It should match the version  number  that  is
       expected by the mail filter application (or by its Milter library).

       Protocol versions:

       2      Use  Sendmail  8  mail  filter  protocol version 2 (default with
              Sendmail version 8.11 .. 8.13 and Postfix version 2.3 ..  2.5).

       3      Use Sendmail 8 mail filter protocol version 3.

       4      Use Sendmail 8 mail filter protocol version 4.

       6      Use Sendmail 8 mail filter  protocol  version  6  (default  with
              Sendmail version 8.14 and Postfix version 2.6).

       Protocol extensions:

       no_header_reply
              Specify this when the Milter application will not reply for each
              individual message header.

       This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP  RCPT  TO command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)
       The macros that are sent to version 3 or higher  Milter  (mail  filter)
       applications  after  an  unknown SMTP command.  See MILTER_README for a
       list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
       The maximal length of MIME multipart boundary strings. The MIME proces-
       sor  is unable to distinguish between boundary strings that do not dif-
       fer in the first $mime_boundary_length_limit characters.

       This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of MIME  related  message
       headers, as described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
       The maximal recursion level that the MIME processor will handle.  Post-
       fix refuses mail that is nested deeper than the specified limit.

       This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
       The minimal time between attempts to deliver a deferred message;  prior
       to Postfix 2.4 the default value was 1000s.

       This  parameter also limits the time an unreachable destination is kept
       in the short-term, in-memory, destination status cache.

       This parameter should be set greater than or equal to $queue_run_delay.
       See also $maximal_backoff_time.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

multi_instance_directories (default: empty)
       An optional list  of  non-default  Postfix  configuration  directories;
       these directories belong to additional Postfix instances that share the
       Postfix executable files and documentation with the default Postfix in-
       stance,  and that are started, stopped, etc., together with the default
       Postfix instance.  Specify a list of pathnames separated  by  comma  or
       whitespace.

       When  $multi_instance_directories is empty, the postfix(1) command runs
       in single-instance mode and operates on a single Postfix instance only.
       Otherwise,  the  postfix(1) command runs in multi-instance mode and in-
       vokes  the  multi-instance  manager  specified   with   the   multi_in-
       stance_wrapper  parameter.  The multi-instance manager in turn executes
       postfix(1) commands for the default instance and for  all  Postfix  in-
       stances in $multi_instance_directories.

       Currently,  this  parameter  setting  is ignored except for the default
       main.cf file.

       This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)
       Allow this  Postfix  instance  to  be  started,  stopped,  etc.,  by  a
       multi-instance  manager.   By  default,  new instances are created in a
       safe state that prevents them from being started  inadvertently.   This
       parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)
       The  optional  instance  group  name  of this Postfix instance. A group
       identifies closely-related Postfix instances  that  the  multi-instance
       manager  can  start, stop, etc., as a unit.  This parameter is reserved
       for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)
       The optional instance name of this Postfix instance. This name  becomes
       also the default value for the syslog_name parameter.

       This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)
       The  pathname  of  a multi-instance manager command that the postfix(1)
       command invokes when the multi_instance_directories parameter value  is
       non-empty.  The  pathname  may be followed by initial command arguments
       separated by whitespace; shell metacharacters such as  quotes  are  not
       supported in this context.

       The  postfix(1) command invokes the manager command with the postfix(1)
       non-option command arguments on the manager command line, and with  all
       installation configuration parameters exported into the manager command
       process environment. The manager command in turn invokes the postfix(1)
       command  for  individual Postfix instances as "postfix -c config_direc-
       tory command".

       This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)
       The numerical Postfix SMTP server response  code  when  a  remote  SMTP
       client request is blocked by the reject_multi_recipient_bounce restric-
       tion.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
       The  list  of  domains that are delivered via the $local_transport mail
       delivery transport. By default this is the  Postfix  local(8)  delivery
       agent  which  looks  up all recipients in /etc/passwd and /etc/aliases.
       The SMTP  server  validates  recipient  addresses  with  $local_recipi-
       ent_maps and rejects non-existent recipients. See also the local domain
       class in the ADDRESS_CLASS_README file.

       The default mydestination value specifies names for the  local  machine
       only.  On a mail domain gateway, you should also include $mydomain.

       The  $local_transport  delivery  method  is  also selected for mail ad-
       dressed to user@[the.net.work.address] of the mail system (the  IP  ad-
       dresses specified with the inet_interfaces and proxy_interfaces parame-
       ters).

       Warnings:

       o      Do not specify the names of virtual domains - those domains  are
              specified elsewhere. See VIRTUAL_README for more information.

       o      Do  not specify the names of domains that this machine is backup
              MX host for. See STANDARD_CONFIGURATION_README for how to set up
              backup MX hosts.

       o      By  default, the Postfix SMTP server rejects mail for recipients
              not listed with the  local_recipient_maps  parameter.   See  the
              postconf(5) manual for a description of the local_recipient_maps
              and unknown_local_recipient_reject_code parameters.

       Specify a list of host or domain names,  "/file/name"  or  "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con-
       tinue long lines by starting the next line with whitespace.

       Examples:

       mydestination = $myhostname, localhost.$mydomain $mydomain
       mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
       The internet domain name of this mail system.  The default  is  to  use
       $myhostname  minus  the  first component, or "localdomain" (Postfix 2.3
       and later).  $mydomain is used as a default value for many  other  con-
       figuration parameters.

       Example:

       mydomain = domain.tld

myhostname (default: see postconf -d output)
       The  internet  hostname  of this mail system. The default is to use the
       fully-qualified domain name (FQDN) from gethostname(), or  to  use  the
       non-FQDN  result  from gethostname() and append ".$mydomain".  $myhost-
       name is used as a default value for many  other  configuration  parame-
       ters.

       Example:

       myhostname = host.example.com

mynetworks (default: see postconf -d output)
       The  list  of  "trusted"  remote SMTP clients that have more privileges
       than "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through
       Postfix.  See the smtpd_relay_restrictions parameter description in the
       postconf(5) manual.

       You can specify the list of "trusted" network addresses by hand or  you
       can let Postfix do it for you (which is the default).  See the descrip-
       tion of the mynetworks_style parameter for more information.

       If you specify the mynetworks list by hand, Postfix ignores the  mynet-
       works_style setting.

       Specify  a list of network addresses or network/netmask patterns, sepa-
       rated by commas and/or whitespace. Continue long lines by starting  the
       next line with whitespace.

       The  netmask specifies the number of bits in the network part of a host
       address.  You can also specify "/file/name" or  "type:table"  patterns.
       A  "/file/name"  pattern  is  replaced  by its contents; a "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).

       The  list  is  matched left to right, and the search stops on the first
       match.  Specify "!pattern" to exclude an address or network block  from
       the  list.  The form "!/file/name" is supported only in Postfix version
       2.4 and later.

       Note 1: Pattern matching of domain names is controlled by  the  or  ab-
       sence of "mynetworks" in the parent_domain_matches_subdomains parameter
       value.

       Note 2: IP version 6 address information must be specified inside [] in
       the  mynetworks  value,  and  in files specified with "/file/name".  IP
       version 6 addresses contain the ":" character, and would  otherwise  be
       confused with a "type:table" pattern.

       Examples:

       mynetworks = 127.0.0.0/8 168.100.189.0/28
       mynetworks = !192.168.0.1, 192.168.0.0/28
       mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
       mynetworks = $config_directory/mynetworks
       mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: Postfix >= 3.0: host, Postfix < 3.0: subnet)
       The  method to generate the default value for the mynetworks parameter.
       This is the list of trusted networks for relay access control etc.

       o      Specify "mynetworks_style = host" when  Postfix  should  "trust"
              only the local machine.

       o      Specify  "mynetworks_style = subnet" when Postfix should "trust"
              remote SMTP clients in the same IP subnetworks as the local  ma-
              chine.   On  Linux,  this  works  correctly only with interfaces
              specified with the "ifconfig" command.

       o      Specify "mynetworks_style = class" when Postfix  should  "trust"
              remote  SMTP  clients in the same IP class A/B/C networks as the
              local machine.  Caution: this may cause Postfix to "trust"  your
              entire  provider's network.  Instead, specify an explicit mynet-
              works list by hand, as described with the mynetworks  configura-
              tion parameter.

myorigin (default: $myhostname)
       The domain name that locally-posted mail appears to come from, and that
       locally posted mail is delivered to. The default, $myhostname, is  ade-
       quate for small sites.  If you run a domain with multiple machines, you
       should (1) change this to $mydomain and (2) set up a domain-wide  alias
       database that aliases each user to user@that.users.mailhost.

       Example:

       myorigin = $mydomain

nested_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of non-MIME message head-
       ers in attached messages, as described in the  header_checks(5)  manual
       page.

       This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
       Sendmail  compatibility  feature  that  specifies  the  location of the
       newaliases(1) command. This command can be used to rebuild the local(8)
       aliases(5) database.

non_fqdn_reject_code (default: 504)
       The  numerical  Postfix SMTP server reply code when a client request is
       rejected by the  reject_non_fqdn_helo_hostname,  reject_non_fqdn_sender
       or reject_non_fqdn_recipient restriction.

non_smtpd_milters (default: empty)
       A  list of Milter (mail filter) applications for new mail that does not
       arrive via the Postfix smtpd(8) server. This includes local  submission
       via the sendmail(1) command line, new mail that arrives via the Postfix
       qmqpd(8) server, and old mail that is re-injected into the  queue  with
       "postsuper  -r".   Specify  space  or  comma as separator. See the MIL-
       TER_README document for details.

       This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
       The list of error classes that are reported to the postmaster. The  de-
       fault  is  to  report  only the most serious problems. The paranoid may
       wish to turn on the policy (UCE and mail relaying) and  protocol  error
       (broken mail software) reports.

       NOTE:  postmaster  notifications  may  contain confidential information
       such as SASL passwords or message content.  It is the  system  adminis-
       trator's responsibility to treat such information with care.

       The error classes are:

       bounce (also implies 2bounce)
              Send  the  postmaster copies of the headers of bounced mail, and
              send transcripts of SMTP sessions when Postfix rejects mail. The
              notification   is   sent  to  the  address  specified  with  the
              bounce_notice_recipient configuration parameter (default:  post-
              master).

       2bounce
              Send undeliverable bounced mail to the postmaster. The notifica-
              tion is sent to  the  address  specified  with  the  2bounce_no-
              tice_recipient configuration parameter (default: postmaster).

       data   Send the postmaster a transcript of the SMTP session with an er-
              ror because a critical data file was unavailable. The  notifica-
              tion  is sent to the address specified with the error_notice_re-
              cipient configuration parameter (default: postmaster).
              This feature is available in Postfix 2.9 and later.

       delay  Send the postmaster copies of the headers of delayed  mail  (see
              delay_warning_time).  The  notification  is  sent to the address
              specified with the delay_notice_recipient configuration  parame-
              ter (default: postmaster).

       policy Send  the  postmaster  a  transcript  of the SMTP session when a
              client request was rejected because of (UCE) policy. The notifi-
              cation  is  sent  to  the  address  specified with the error_no-
              tice_recipient configuration parameter (default: postmaster).

       protocol
              Send the postmaster a transcript of the SMTP session in case  of
              client  or  server  protocol errors. The notification is sent to
              the address specified with the error_notice_recipient configura-
              tion parameter (default: postmaster).

       resource
              Inform  the  postmaster  of  mail  not delivered due to resource
              problems.  The notification is sent  to  the  address  specified
              with  the  error_notice_recipient  configuration  parameter (de-
              fault: postmaster).

       software
              Inform the postmaster of mail  not  delivered  due  to  software
              problems.   The  notification  is  sent to the address specified
              with the  error_notice_recipient  configuration  parameter  (de-
              fault: postmaster).

       Examples:

       notify_classes = bounce, delay, policy, protocol, resource, software
       notify_classes = 2bounce, resource, software

nullmx_reject_code (default: 556)
       The  numerical reply code when the Postfix SMTP server rejects a sender
       or recipient address because its domain has a nullmx DNS record (an  MX
       record  with  an  empty  hostname). This is one of the possible replies
       from  the  restrictions  reject_unknown_sender_domain  and   reject_un-
       known_recipient_domain.

       This feature is available in Postfix 3.0 and later.

openssl_path (default: openssl)
       The  location  of the OpenSSL command line program openssl(1).  This is
       used by the "postfix tls" command to create private  keys,  certificate
       signing  requests,  self-signed certificates, and to compute public key
       digests for DANE TLSA records.  In  multi-instance  environments,  this
       parameter  is  always  determined from the configuration of the default
       Postfix instance.

       Example:

           /etc/postfix/main.cf:
               # NetBSD pkgsrc:
               openssl_path = /usr/pkg/bin/openssl
               # Local build:
               openssl_path = /usr/local/bin/openssl

       This feature is available in Postfix 3.1 and later.

owner_request_special (default: yes)
       Enable special treatment for owner-listname entries in  the  aliases(5)
       file,  and  don't split owner-listname and listname-request address lo-
       calparts when the recipient_delimiter is set to "-".  This  feature  is
       useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
       A list of Postfix features where the pattern "example.com" also matches
       subdomains of example.com, instead of  requiring  an  explicit  ".exam-
       ple.com"  pattern.   This  is planned backwards compatibility:  eventu-
       ally, all Postfix features are expected  to  require  explicit  ".exam-
       ple.com" style patterns when you really want to match subdomains.

       The following Postfix feature names are supported.

       Postfix version 1.0 and later
              debug_peer_list,     fast_flush_domains,     mynetworks,    per-
              mit_mx_backup_networks, relay_domains, transport_maps

       Postfix version 1.1 and later
              qmqpd_authorized_clients, smtpd_access_maps,

       Postfix version 2.8 and later
              postscreen_access_list

       Postfix version 3.0 and later
              smtpd_client_event_limit_exceptions

permit_mx_backup_networks (default: empty)
       Restrict the use of the permit_mx_backup SMTP access  feature  to  only
       domains  whose primary MX hosts match the listed networks.  The parame-
       ter value syntax is the same as with the  mynetworks  parameter;  note,
       however, that the default value is empty.

       Pattern  matching  of domain names is controlled by the presence or ab-
       sence of "permit_mx_backup_networks" in the  parent_domain_matches_sub-
       domains parameter value.

pickup_service_name (default: pickup)
       The  name  of  the  pickup(8) service. This service picks up local mail
       submissions from the Postfix maildrop queue.

       This feature is available in Postfix 2.0 and later.

pipe_delivery_status_filter (default: $default_delivery_status_filter)
       Optional filter for the pipe(8) delivery agent to change  the  delivery
       status  code or explanatory text of successful or unsuccessful deliver-
       ies.  See default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

plaintext_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a request  is  re-
       jected by the reject_plaintext_session restriction.

       This feature is available in Postfix 2.3 and later.

postlog_service_name (default: postlog)
       The  name  of the postlogd(8) service entry in master.cf.  This service
       appends logfile records to the file specified with the maillog_file pa-
       rameter.

       This feature is available in Postfix 3.4 and later.

postlogd_watchdog_timeout (default: 10s)
       How  much  time a postlogd(8) process may take to process a request be-
       fore it is terminated by a built-in watchdog timer. This  is  a  safety
       mechanism that prevents postlogd(8) from becoming non-responsive due to
       a bug in Postfix itself or in system software. This limit cannot be set
       under 10s.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 3.4 and later.

postmulti_control_commands (default: reload flush)
       The  postfix(1)  commands that the postmulti(1) instance manager treats
       as "control" commands, that operate on  running  instances.  For  these
       commands, disabled instances are skipped.

       This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)
       The  postfix(1)  commands that the postmulti(1) instance manager treats
       as  "start"  commands.  For  these  commands,  disabled  instances  are
       "checked"  rather  than  "started", and failure to "start" a member in-
       stance of an instance group will abort the start-up of later instances.

       This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)
       The postfix(1) commands that the postmulti(1) instance  manager  treats
       as "stop" commands. For these commands, disabled instances are skipped,
       and enabled instances are processed in reverse order.

       This feature is available in Postfix 2.6 and later.

postscreen_access_list (default: permit_mynetworks)
       Permanent  white/blacklist  for  remote  SMTP  client   IP   addresses.
       postscreen(8) searches this list immediately after a remote SMTP client
       connects.  Specify a comma- or whitespace-separated  list  of  commands
       (in  upper  or  lower case) or lookup tables. The search stops upon the
       first command that fires for the client IP address.

        permit_mynetworks
              Whitelist the client and terminate the search if the  client  IP
              address  matches  $mynetworks.  Do not subject the client to any
              before/after 220 greeting tests.  Pass  the  connection  immedi-
              ately to a Postfix SMTP server process.
              Pattern  matching  of domain names is controlled by the presence
              or  absence  of  "postscreen_access_list"  in   the   parent_do-
              main_matches_subdomains parameter value.

        type:table
              Query the specified lookup table. Each table lookup result is an
              access list, except that access  lists  inside  a  table  cannot
              specify type:table entries.
              To  discourage  the use of hash, btree, etc. tables, there is no
              support for substring matching like smtpd(8).  Use  CIDR  tables
              instead.

        permit
              Whitelist  the  client  and terminate the search. Do not subject
              the client to any before/after 220 greeting tests. Pass the con-
              nection immediately to a Postfix SMTP server process.

        reject
              Blacklist  the  client  and  terminate  the  search. Subject the
              client to  the  action  configured  with  the  postscreen_black-
              list_action configuration parameter.

        dunno All  postscreen(8)  access lists implicitly have this command at
              the end.
              When  dunno is executed inside a lookup table, return  from  the
              lookup table and evaluate the next command.
              When   dunno   is executed outside a lookup table, terminate the
              search, and subject the client to  the  configured  before/after
              220 greeting tests.

       Example:

       /etc/postfix/main.cf:
           postscreen_access_list = permit_mynetworks,
               cidr:/etc/postfix/postscreen_access.cidr
           postscreen_blacklist_action = enforce

       /etc/postfix/postscreen_access.cidr:
           # Rules are evaluated in the order as specified.
           # Blacklist 192.168.* except 192.168.0.1.
           192.168.0.1         dunno
           192.168.0.0/16      reject

       This feature is available in Postfix 2.8.

postscreen_bare_newline_action (default: ignore)
       The  action  that postscreen(8) takes when a remote SMTP client sends a
       bare newline character, that is, a newline not preceded by carriage re-
       turn.  Specify one of the following:

       ignore Ignore  the failure of this test. Allow other tests to complete.
              Do not repeat this test before some the result from  some  other
              test  expires.  This option is useful for testing and collecting
              statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to  deliver  mail
              with  a 550 SMTP reply, and log the helo/sender/recipient infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP  reply.  Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_enable (default: no)
       Enable  "bare newline" SMTP protocol tests in the postscreen(8) server.
       These tests are expensive: a remote SMTP client must  disconnect  after
       it passes the test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_ttl (default: 30d)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful "bare newline" SMTP protocol test. During this time, the client
       IP  address  is  excluded from this test. The default is long because a
       remote SMTP client must disconnect after it passes the test, before  it
       can talk to a real Postfix SMTP server.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_blacklist_action (default: ignore)
       The action that postscreen(8) takes when a remote SMTP client is perma-
       nently blacklisted with the postscreen_access_list parameter.   Specify
       one of the following:

       ignore (default)
              Ignore  this result. Allow other tests to complete.  Repeat this
              test the next time the client connects.  This option  is  useful
              for testing and collecting statistics without blocking mail.

       enforce
              Allow  other  tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient  infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_cache_cleanup_interval (default: 12h)
       The amount of time between postscreen(8)  cache  cleanup  runs.   Cache
       cleanup  increases  the load on the cache database and should therefore
       not be run frequently. This feature requires that  the  cache  database
       supports  the "delete" and "sequence" operators.  Specify a zero inter-
       val to disable cache cleanup.

       After each cache cleanup run, the postscreen(8) daemon logs the  number
       of  entries  that were retained and dropped. A cleanup run is logged as
       "partial" when the daemon  terminates  early  after  "postfix  reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_cache_map (default: btree:$data_directory/postscreen_cache)
       Persistent storage for the postscreen(8) server decisions.

       To  share  a  postscreen(8)  cache  between  multiple postscreen(8) in-
       stances, use "postscreen_cache_map = proxy:btree:/path/to/file".   This
       requires  Postfix version 2.9 or later; earlier proxymap(8) implementa-
       tions don't support cache cleanup. For an alternative approach see  the
       memcache_table(5) manpage.

       This feature is available in Postfix 2.8.

postscreen_cache_retention_time (default: 7d)
       The  amount  of time that postscreen(8) will cache an expired temporary
       whitelist entry before it is removed. This prevents clients from  being
       logged  as "NEW" just because their cache entry expired an hour ago. It
       also prevents the cache from filling up with clients that  passed  some
       deep protocol test once and never came back.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_client_connection_count_limit    (default:    $smtpd_client_connec-
       tion_count_limit)
       How many simultaneous connections any remote SMTP client is allowed  to
       have  with the postscreen(8) daemon. By default, this limit is the same
       as with the Postfix SMTP server. Note that the triage process can  take
       several  seconds,  with  the time spent in postscreen_greet_wait delay,
       and with the time spent talking to  the  postscreen(8)  built-in  dummy
       SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_command_count_limit (default: 20)
       The  limit  on  the  total  number  of  commands  per  SMTP session for
       postscreen(8)'s built-in SMTP protocol engine.  This SMTP engine defers
       or  rejects all attempts to deliver mail, therefore there is no need to
       enforce separate limits on the number of junk commands and  error  com-
       mands.

       This feature is available in Postfix 2.8.

postscreen_command_filter (default: $smtpd_command_filter)
       A  mechanism  to  transform  commands  from  remote  SMTP clients.  See
       smtpd_command_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_command_time_limit (default: normal: 300s, overload: 10s)
       The time limit to read an  entire  command  line  with  postscreen(8)'s
       built-in SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_disable_vrfy_command (default: $disable_vrfy_command)
       Disable  the  SMTP  VRFY command in the postscreen(8) daemon.  See dis-
       able_vrfy_command for details.

       This feature is available in Postfix 2.8.

postscreen_discard_ehlo_keyword_address_maps       (default:       $smtpd_dis-
       card_ehlo_keyword_address_maps)
       Lookup tables, indexed by the remote SMTP client address, with case in-
       sensitive lists of EHLO keywords  (pipelining,  starttls,  auth,  etc.)
       that  the  postscreen(8) server will not send in the EHLO response to a
       remote SMTP client. See smtpd_discard_ehlo_keywords for  details.   The
       table is not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.8 and later.

postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords)
       A  case  insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the postscreen(8) server will not send in the EHLO  response
       to a remote SMTP client. See smtpd_discard_ehlo_keywords for details.

       This feature is available in Postfix 2.8 and later.

postscreen_dnsbl_action (default: ignore)
       The  action  that  postscreen(8) takes when a remote SMTP client's com-
       bined DNSBL score is equal to or greater than a threshold  (as  defined
       with  the postscreen_dnsbl_sites and postscreen_dnsbl_threshold parame-
       ters).  Specify one of the following:

       ignore (default)
              Ignore the failure of this test. Allow other tests to  complete.
              Repeat this test the next time the client connects.  This option
              is useful for testing and collecting statistics without blocking
              mail.

       enforce
              Allow  other  tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient  infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_max_ttl                                             (default:
       ${postscreen_dnsbl_ttl?{$postscreen_dnsbl_ttl}:{1}}h)
       The  maximum amount of time that postscreen(8) will use the result from
       a successful DNS-based reputation test before a client  IP  address  is
       required  to pass that test again. If the DNS reply specifies a shorter
       TTL value, that value will be used unless  it  would  be  smaller  than
       postscreen_dnsbl_min_ttl.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This  feature is available in Postfix 3.1. The default setting is back-
       wards-compatible with older Postfix versions.

postscreen_dnsbl_min_ttl (default: 60s)
       The minimum amount of time that postscreen(8) will use the result  from
       a  successful  DNS-based  reputation test before a client IP address is
       required to pass that test again. If the DNS reply specifies  a  larger
       TTL  value,  that  value  will  be  used unless it would be larger than
       postscreen_dnsbl_max_ttl.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 3.1.

postscreen_dnsbl_reply_map (default: empty)
       A mapping from actual DNSBL domain name which includes a  secret  pass-
       word,  to the DNSBL domain name that postscreen will reply with when it
       rejects mail.  When no mapping is found, the actual DNSBL  domain  will
       be used.

       For maximal stability it is best to use a file that is read into memory
       such as pcre:, regexp: or texthash: (texthash: is similar to hash:, ex-
       cept a) there is no need to run postmap(1) before the file can be used,
       and b) texthash: does not detect changes after the file is read).

       Example:

       /etc/postfix/main.cf:
           postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply

       /etc/postfix/dnsbl_reply:
          secret.zen.spamhaus.org      zen.spamhaus.org

       This feature is available in Postfix 2.8.

postscreen_dnsbl_sites (default: empty)
       Optional list of DNS white/blacklist domains, filters and  weight  fac-
       tors.  When  the  list  is  non-empty, the dnsblog(8) daemon will query
       these domains with  the  IP  addresses  of  remote  SMTP  clients,  and
       postscreen(8)  will  update  an  SMTP  client's  DNSBL  score with each
       non-error reply.

       Caution: when postscreen rejects mail, it replies with the DNSBL domain
       name. Use the postscreen_dnsbl_reply_map feature to hide "password" in-
       formation in DNSBL domain names.

       When a client's score is equal to or greater than the threshold  speci-
       fied  with  postscreen_dnsbl_threshold, postscreen(8) can drop the con-
       nection with the remote SMTP client.

       Specify a list of domain=filter*weight entries, separated by  comma  or
       whitespace.

       o      When  no  "=filter"  is  specified,  postscreen(8)  will use any
              non-error DNSBL reply.  Otherwise, postscreen(8) uses only DNSBL
              replies  that match the filter. The filter has the form d.d.d.d,
              where each d is a number, or a pattern inside []  that  contains
              one or more ";"-separated numbers or number..number ranges.

       o      When no "*weight" is specified, postscreen(8) increments the re-
              mote SMTP client's DNSBL score by 1.  Otherwise, the weight must
              be  an  integral  number,  and  postscreen(8) adds the specified
              weight to the remote SMTP client's DNSBL score.  Specify a nega-
              tive number for whitelisting.

       o      When  one  postscreen_dnsbl_sites  entry produces multiple DNSBL
              responses, postscreen(8) applies the weight at most once.

       Examples:

       To use example.com as a high-confidence blocklist, and  to  block  mail
       with example.net and example.org only when both agree:

       postscreen_dnsbl_threshold = 2
       postscreen_dnsbl_sites = example.com*2, example.net, example.org

       To filter only DNSBL replies containing 127.0.0.4:

       postscreen_dnsbl_sites = example.com=127.0.0.4

       This feature is available in Postfix 2.8.

postscreen_dnsbl_threshold (default: 1)
       The  inclusive  lower bound for blocking a remote SMTP client, based on
       its combined DNSBL score as defined with the postscreen_dnsbl_sites pa-
       rameter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_timeout (default: 10s)
       The  time  limit  for DNSBL or DNSWL lookups. This is separate from the
       timeouts in the dnsblog(8) daemon  which  are  defined  by  system  re-
       solver(3) routines.

       This feature is available in Postfix 3.0.

postscreen_dnsbl_ttl (default: 1h)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful DNS-based reputation test before a client  IP  address  is  re-
       quired to pass that test again.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This  feature  is  available  in  Postfix  2.8-3.0.  It was replaced by
       postscreen_dnsbl_max_ttl in Postfix 3.1.

postscreen_dnsbl_whitelist_threshold (default: 0)
       Allow a remote SMTP client to skip "before" and  "after  220  greeting"
       protocol  tests,  based on its combined DNSBL score as defined with the
       postscreen_dnsbl_sites parameter.

       Specify a negative value to enable this feature. When a  client  passes
       the  postscreen_dnsbl_whitelist_threshold  without  having failed other
       tests, all pending or disabled tests are flagged as  completed  with  a
       time-to-live  value equal to postscreen_dnsbl_ttl.  When a test was al-
       ready completed, its time-to-live value is updated if it was less  than
       postscreen_dnsbl_ttl.

       This feature is available in Postfix 2.11.

postscreen_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory  TLS:  announce  STARTTLS support to remote SMTP clients, and
       require that clients  use  TLS  encryption.   See  smtpd_postscreen_en-
       force_tls for details.

       This  feature  is  available in Postfix 2.8 and later.  Preferably, use
       postscreen_tls_security_level instead.

postscreen_expansion_filter (default: see postconf -d output)
       List of characters that are permitted in  postscreen_reject_footer  at-
       tribute expansions.  See smtpd_expansion_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_forbidden_commands (default: $smtpd_forbidden_commands)
       List  of  commands that the postscreen(8) server considers in violation
       of the SMTP protocol.  See  smtpd_forbidden_commands  for  syntax,  and
       postscreen_non_smtp_command_action for possible actions.

       This feature is available in Postfix 2.8.

postscreen_greet_action (default: ignore)
       The  action  that  postscreen(8) takes when a remote SMTP client speaks
       before   its   turn   within    the    time    specified    with    the
       postscreen_greet_wait parameter.  Specify one of the following:

       ignore (default)
              Ignore  the failure of this test. Allow other tests to complete.
              Repeat this test the next time the client connects.  This option
              is useful for testing and collecting statistics without blocking
              mail.

       enforce
              Allow other tests to complete. Reject attempts to  deliver  mail
              with  a 550 SMTP reply, and log the helo/sender/recipient infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP  reply.  Repeat
              this test the next time the client connects.

       In either case, postscreen(8) will not whitelist the remote SMTP client
       IP address.

       This feature is available in Postfix 2.8.

postscreen_greet_banner (default: $smtpd_banner)
       The  text  in  the  optional   "220-text..."   server   response   that
       postscreen(8)  sends  ahead  of  the  real  Postfix  SMTP server's "220
       text..." response, in an attempt to confuse bad SMTP  clients  so  that
       they  speak  before  their turn (pre-greet).  Specify an empty value to
       disable this feature.

       This feature is available in Postfix 2.8.

postscreen_greet_ttl (default: 1d)
       The amount of time that postscreen(8) will use the result from  a  suc-
       cessful  PREGREET  test. During this time, the client IP address is ex-
       cluded from this test. The default is relatively short, because a  good
       client can immediately talk to a real Postfix SMTP server.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: normal: 6s, overload: 2s)
       The  amount  of time that postscreen(8) will wait for an SMTP client to
       send a command before its turn, and for DNS blocklist lookup results to
       arrive  (default:  up to 2 seconds under stress, up to 6 seconds other-
       wise).

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_helo_required (default: $smtpd_helo_required)
       Require  that a remote SMTP client sends HELO or EHLO before commencing
       a MAIL transaction.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_action (default: drop)
       The action that postscreen(8) takes when a  remote  SMTP  client  sends
       non-SMTP  commands  as specified with the postscreen_forbidden_commands
       parameter.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to  complete.
              Do  not  repeat this test before some the result from some other
              test expires.  This option is useful for testing and  collecting
              statistics without blocking mail permanently.

       enforce
              Allow  other  tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient  infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects. This action is  the
              same  as with the Postfix SMTP server's smtpd_forbidden_commands
              feature.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_enable (default: no)
       Enable "non-SMTP command" tests  in  the  postscreen(8)  server.  These
       tests are expensive: a client must disconnect after it passes the test,
       before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from  a  suc-
       cessful  "non_smtp_command"  SMTP  protocol test. During this time, the
       client IP address is excluded from this test. The default is  long  be-
       cause  a client must disconnect after it passes the test, before it can
       talk to a real Postfix SMTP server.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_pipelining_action (default: enforce)
       The action that postscreen(8) takes when a  remote  SMTP  client  sends
       multiple  commands  instead  of sending one command and waiting for the
       server to respond.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to  complete.
              Do  not  repeat this test before some the result from some other
              test expires.  This option is useful for testing and  collecting
              statistics without blocking mail permanently.

       enforce
              Allow  other  tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient  infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_pipelining_enable (default: no)
       Enable "pipelining" SMTP protocol tests in  the  postscreen(8)  server.
       These  tests  are  expensive:  a  good  client must disconnect after it
       passes the test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_pipelining_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from  a  suc-
       cessful  "pipelining"  SMTP protocol test. During this time, the client
       IP address is excluded from this test. The default is  long  because  a
       good  client  must  disconnect  after it passes the test, before it can
       talk to a real Postfix SMTP server.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_post_queue_limit (default: $default_process_limit)
       The number of clients that can be waiting for service from a real Post-
       fix  SMTP server process. When this queue is full, all clients will re-
       ceive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_pre_queue_limit (default: $default_process_limit)
       The number of non-whitelisted clients that can be waiting for  a  deci-
       sion  whether they will receive service from a real Postfix SMTP server
       process. When this queue is full, all non-whitelisted clients will  re-
       ceive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_reject_footer (default: $smtpd_reject_footer)
       Optional  information that is appended after a 4XX or 5XX postscreen(8)
       server response. See smtpd_reject_footer for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_reject_footer_maps (default: $smtpd_reject_footer_maps)
       Optional lookup table for information that is appended after a  4XX  or
       5XX  postscreen(8)  server  response.  See smtpd_reject_footer_maps for
       further details.

       This feature is available in Postfix 3.4 and later.

postscreen_tls_security_level (default: $smtpd_tls_security_level)
       The SMTP TLS security  level  for  the  postscreen(8)  server;  when  a
       non-empty  value  is  specified, this overrides the obsolete parameters
       postscreen_use_tls  and  postscreen_enforce_tls.  See   smtpd_tls_secu-
       rity_level for details.

       This feature is available in Postfix 2.8 and later.

postscreen_upstream_proxy_protocol (default: empty)
       The  name  of  the proxy protocol used by an optional before-postscreen
       proxy agent. When a proxy agent is used, this  protocol  conveys  local
       and  remote  address  and  port  information.  Specify  "postscreen_up-
       stream_proxy_protocol = haproxy" to enable the haproxy protocol.

       This feature is available in Postfix 2.10 and later.

postscreen_upstream_proxy_timeout (default: 5s)
       The time limit for the proxy protocol specified with the postscreen_up-
       stream_proxy_protocol parameter.

       This feature is available in Postfix 2.10 and later.

postscreen_use_tls (default: $smtpd_use_tls)
       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients,
       but do not require that clients use TLS encryption.

       This feature is available in Postfix 2.8 and  later.   Preferably,  use
       postscreen_tls_security_level instead.

postscreen_watchdog_timeout (default: 10s)
       How  much  time a postscreen(8) process may take to respond to a remote
       SMTP client command or to perform a cache operation before it is termi-
       nated  by  a  built-in watchdog timer.  This is a safety mechanism that
       prevents postscreen(8) from becoming non-responsive due  to  a  bug  in
       Postfix itself or in system software.  To avoid false alarms and unnec-
       essary cache corruption this limit cannot be set under 10s.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_whitelist_interfaces (default: static:all)
       A  list  of  local  postscreen(8)   server   IP   addresses   where   a
       non-whitelisted remote SMTP client can obtain postscreen(8)'s temporary
       whitelist status. This status is required before the client can talk to
       a  Postfix  SMTP  server  process.   By  default,  a  client can obtain
       postscreen(8)'s whitelist status on any local postscreen(8)  server  IP
       address.

       When postscreen(8) listens on both primary and backup MX addresses, the
       postscreen_whitelist_interfaces parameter can be configured to give the
       temporary  whitelist status only when a client connects to a primary MX
       address. Once a client is whitelisted it can talk  to  a  Postfix  SMTP
       server on any address. Thus, clients that connect only to backup MX ad-
       dresses will never become whitelisted, and will  never  be  allowed  to
       talk to a Postfix SMTP server process.

       Specify  a list of network addresses or network/netmask patterns, sepa-
       rated by commas and/or whitespace. The netmask specifies the number  of
       bits  in  the  network  part  of a host address. Continue long lines by
       starting the next line with whitespace.

       You  can  also  specify  "/file/name"  or  "type:table"  patterns.    A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when a table entry matches a lookup string (the lookup
       result is ignored).

       The  list  is  matched left to right, and the search stops on the first
       match. Specify "!pattern" to exclude an address or network  block  from
       the list.

       Note:  IP  version 6 address information must be specified inside [] in
       the postscreen_whitelist_interfaces value, and in files specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

       Example:

       /etc/postfix/main.cf:
           # Don't whitelist connections to the backup IP address.
           postscreen_whitelist_interfaces = !168.100.189.8, static:all

       This feature is available in Postfix 2.9 and later.

prepend_delivered_header (default: command, file, forward)
       The message delivery contexts where the Postfix local(8) delivery agent
       prepends a Delivered-To:  message header with the address that the mail
       was delivered to. This information is used for mail delivery  loop  de-
       tection.

       By  default,  the Postfix local delivery agent prepends a Delivered-To:
       header when forwarding mail and when delivering to file  (mailbox)  and
       command.  Turning  off the Delivered-To: header when forwarding mail is
       not recommended.

       Specify zero or more of forward, file, or command.

       Example:

       prepend_delivered_header = forward

process_id (read-only)
       The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
       The location of Postfix PID files relative to  $queue_directory.   This
       is a read-only parameter.

process_name (read-only)
       The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
       What  address  lookup  tables copy an address extension from the lookup
       key to the lookup result.

       For  example,  with  a  virtual(5)  mapping  of   "joe@example.com   =_
       joe.user@example.net",  the address "joe+foo@example.com" would rewrite
       to "joe.user+foo@example.net".

       Specify zero or more of canonical, virtual, alias, forward, include  or
       generic.  These  cause address extension propagation with canonical(5),
       virtual(5), and aliases(5) maps, with local(8) .forward  and  :include:
       file lookups, and with smtp(8) generic maps, respectively.

       Note:  enabling this feature for types other than canonical and virtual
       is likely to cause problems when mail is forwarded to other sites,  es-
       pecially with mail that is sent to a mailing list exploder address.

       Examples:

       propagate_unmatched_extensions = canonical, virtual, alias,
               forward, include
       propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
       The  network interface addresses that this mail system receives mail on
       by way of a proxy or network address translation unit.

       This feature is available in Postfix 2.0 and later.

       You must specify your "outside" proxy/NAT addresses when your system is
       a  backup MX host for other domains, otherwise mail delivery loops will
       happen when the primary MX host is down.

       Example:

       proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access  for
       the read-only service.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma.  Table references that don't begin with proxy: are ignored.

       This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access  for
       the  read-write  service.  Postfix-owned local database files should be
       stored under the Postfix-owned data_directory.  Table  references  that
       don't begin with proxy: are ignored.

       This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)
       The  name of the proxymap read-only table lookup service.  This service
       is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)
       The name of the proxywrite read-write table lookup service.  This  ser-
       vice is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)
       The minimal delay between warnings that a specific destination is clog-
       ging up the Postfix active queue. Specify 0 to disable.

       This feature is enabled with the helpful_warnings parameter.

       This feature is available in Postfix 2.0 and later.

qmgr_daemon_timeout (default: 1000s)
       How much time a Postfix queue manager process may take to handle a  re-
       quest before it is terminated by a built-in watchdog timer.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_fudge_factor (default: 100)
       Obsolete feature: the percentage of delivery resources that a busy mail
       system will use up for delivery of a large mailing  list message.

       This feature exists only in the oqmgr(8) old queue manager. The current
       queue manager solves the problem in a better way.

qmgr_ipc_timeout (default: 60s)
       The time limit for the queue manager to  send  or  receive  information
       over an internal communication channel.  The purpose is to break out of
       deadlock situations. If the time limit is exceeded the software  either
       retries or aborts the operation.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_message_active_limit (default: 20000)
       The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
       The maximal number of recipients held in memory by  the  Postfix  queue
       manager,  and the maximal size of the short-term, in-memory "dead" des-
       tination status cache.

qmgr_message_recipient_minimum (default: 10)
       The minimal number of in-memory recipients for any message. This  takes
       priority  over  any  other in-memory recipient limits (i.e., the global
       qmgr_message_recipient_limit and the per transport _recipient_limit) if
       necessary. The minimum value allowed for this parameter is 1.

qmqpd_authorized_clients (default: empty)
       What  remote  QMQP  clients  are allowed to connect to the Postfix QMQP
       server port.

       By default, no client is allowed to use the service.  This  is  because
       the QMQP server will relay mail to any destination.

       Specify  a  list  of  client  patterns. A list pattern specifies a host
       name, a domain name, an internet address, or  a  network/mask  pattern,
       where  the mask specifies the number of bits in the network part.  When
       a pattern specifies a file name, its contents are substituted  for  the
       file  name; when a pattern is a "type:table" table specification, table
       lookup is used instead.

       Patterns are separated by whitespace and/or commas. In order to reverse
       the  result,  precede a pattern with an exclamation point (!). The form
       "!/file/name" is supported only in Postfix version 2.4 and later.

       Pattern matching of domain names is controlled by the presence  or  ab-
       sence of "qmqpd_authorized_clients" in the parent_domain_matches_subdo-
       mains parameter value.

       Example:

       qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)
       Enable logging of the remote QMQP client port in addition to the  host-
       name and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)
       How  long  the Postfix QMQP server will pause before sending a negative
       reply to the remote QMQP client. The purpose is to slow  down  confused
       or malicious clients.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

qmqpd_timeout (default: 300s)
       The time limit for sending or receiving information over  the  network.
       If  a  read or write operation blocks for more than $qmqpd_timeout sec-
       onds the Postfix QMQP server gives up and disconnects.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

queue_directory (default: see postconf -d output)
       The location of the Postfix top-level queue directory. This is the root
       directory of Postfix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
       The maximal number of (name=value) attributes that may be stored  in  a
       Postfix queue file. The limit is enforced by the cleanup(8) server.

       This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
       The minimal amount of free space in bytes in the queue file system that
       is needed to receive mail.  This is currently used by the Postfix  SMTP
       server to decide if it will accept any mail at all.

       By default, the Postfix SMTP server rejects MAIL FROM commands when the
       amount of free space is less than 1.5*$message_size_limit (Postfix ver-
       sion  2.1  and  later).   To specify a higher minimum free space limit,
       specify a queue_minfree value that is at least 1.5*$message_size_limit.

       With Postfix versions 2.0 and earlier, a queue_minfree  value  of  zero
       means there is no minimum required amount of free space.

queue_run_delay (default: 300s)
       The  time  between  deferred queue scans by the queue manager; prior to
       Postfix 2.4 the default value was 1000s.

       This parameter should be set  less  than  or  equal  to  $minimal_back-
       off_time. See also $maximal_backoff_time.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

queue_service_name (default: qmgr)
       The name of the qmgr(8) service. This service manages the Postfix queue
       and schedules delivery requests.

       This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
       Optional  lookup tables with RBL response templates. The tables are in-
       dexed by the RBL domain name. By default, Postfix uses the default tem-
       plate  as specified with the default_rbl_reply configuration parameter.
       See there for a discussion of the syntax of RBL reply templates.

       This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
       The location of Postfix README files that describe how to  build,  con-
       figure or operate a specific Postfix subsystem or feature.

receive_override_options (default: empty)
       Enable  or disable recipient validation, built-in content filtering, or
       address mapping. Typically, these are specified in  master.cf  as  com-
       mand-line arguments for the smtpd(8), qmqpd(8) or pickup(8) daemons.

       Specify  zero  or  more of the following options.  The options override
       main.cf settings and are either implemented by smtpd(8),  qmqpd(8),  or
       pickup(8) themselves, or they are forwarded to the cleanup server.

       no_unknown_recipient_checks
              Do  not  try  to  reject  unknown recipients (SMTP server only).
              This is typically specified AFTER an external content filter.

       no_address_mappings
              Disable canonical address mapping, virtual alias map  expansion,
              address  masquerading, and automatic BCC (blind carbon-copy) re-
              cipients. This is typically specified BEFORE an external content
              filter.

       no_header_body_checks
              Disable header/body_checks. This is typically specified AFTER an
              external content filter.

       no_milters
              Disable Milter (mail filter)  applications.  This  is  typically
              specified AFTER an external content filter.

       Note: when the "BEFORE content filter" receive_override_options setting
       is specified in the main.cf file, specify the  "AFTER  content  filter"
       receive_override_options setting in master.cf (and vice versa).

       Examples:

       receive_override_options =
           no_unknown_recipient_checks, no_header_body_checks
       receive_override_options = no_address_mappings

       This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
       Optional  BCC (blind carbon-copy) address lookup tables, indexed by re-
       cipient address.  The BCC address (multiple results are not  supported)
       is added when mail enters from outside of Postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       The table search order is as follows:

       o      Look  up  the  "user+extension@domain.tld" address including the
              optional address extension.

       o      Look up the "user@domain.tld" address without the  optional  ad-
              dress extension.

       o      Look up the "user+extension" address local part when the recipi-
              ent domain equals $myorigin, $mydestination, $inet_interfaces or
              $proxy_interfaces.

       o      Look  up the "user" address local part when the recipient domain
              equals $myorigin, $mydestination, $inet_interfaces or $proxy_in-
              terfaces.

       o      Look up the "@domain.tld" part.

       Note:  with Postfix 2.3 and later the BCC address is added as if it was
       specified with NOTIFY=NONE. The sender will not be  notified  when  the
       BCC  address  is undeliverable, as long as all down-stream software im-
       plements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will  unconditionally  be
       notified when the BCC address is undeliverable.

       Note:  automatic  BCC  recipients  are  produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are  not  generated  after
       Postfix  forwards  mail internally, or after Postfix generates mail it-
       self.

       Example:

       recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

       After a change, run "postmap /etc/postfix/recipient_bcc".

       This feature is available in Postfix 2.1 and later.

recipient_canonical_classes (default: envelope_recipient, header_recipient)
       What addresses are subject to recipient_canonical_maps address mapping.
       By  default, recipient_canonical_maps address mapping is applied to en-
       velope recipient addresses, and to header recipient addresses.

       Specify one or more of: envelope_recipient, header_recipient

       This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
       Optional address mapping lookup tables for envelope and header  recipi-
       ent  addresses.  The table format and lookups are documented in canoni-
       cal(5).

       Note: $recipient_canonical_maps is processed before $canonical_maps.

       Example:

       recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)
       The set of characters that can separate a user name from its  extension
       (example:  user+foo), or a .forward file name from its extension (exam-
       ple: .forward+foo).  Basically, the software tries user+foo  and  .for-
       ward+foo  before  trying user and .forward.  This implementation recog-
       nizes one delimiter character and one extension per  email  address  or
       .forward file name.

       When  the recipient_delimiter set contains multiple characters (Postfix
       2.11 and later), a user name or .forward file name  is  separated  from
       its  extension by the first character that matches the recipient_delim-
       iter set.

       See canonical(5), local(8), relocated(5) and virtual(5) for the effects
       of  recipient_delimiter  on lookups in aliases, canonical, virtual, and
       relocated maps, and see  the  propagate_unmatched_extensions  parameter
       for propagating an extension from one email address to another.

       When used in command_execution_directory, forward_path, or luser_relay,
       ${recipient_delimiter} is replaced with the actual recipient  delimiter
       that was found in the recipient email address (Postfix 2.11 and later),
       or it is replaced with the main.cf recipient_delimiter parameter  value
       (Postfix 2.10 and earlier).

       The  recipient_delimiter  is  not applied to the mailer-daemon address,
       the postmaster address, or the double-bounce address. With the  default
       "owner_request_special  = yes" setting, the recipient_delimiter is also
       not applied to addresses with the special "owner-" prefix or  the  spe-
       cial "-request" suffix.

       Examples:

       # Handle Postfix-style extensions.
       recipient_delimiter = +

       # Handle both Postfix and qmail extensions (Postfix 2.11 and later).
       recipient_delimiter = +-

       # Use .forward for mail without address extension, and for mail with
       # an unrecognized address extension.
       forward_path = $home/.forward${recipient_delimiter}${extension},
           $home/.forward

reject_code (default: 554)
       The  numerical  Postfix  SMTP  server  response code when a remote SMTP
       client request is rejected by the "reject" restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

reject_tempfail_action (default: defer_if_permit)
       The  Postfix  SMTP server's action when a reject-type restriction fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP client request immediately. With the default "defer_if_permit" ac-
       tion, the Postfix SMTP server continues to look  for  opportunities  to
       reject  mail,  and defers the client request only if it would otherwise
       be accepted.

       For finer control, see:  unverified_recipient_tempfail_action,  unveri-
       fied_sender_tempfail_action,  unknown_address_tempfail_action,  and un-
       known_helo_hostname_tempfail_action.

       This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)
       List of tables with remote SMTP client-certificate fingerprints or pub-
       lic key fingerprints (Postfix 2.9 and later) for which the Postfix SMTP
       server will allow access with the permit_tls_clientcerts feature.   The
       fingerprint  digest algorithm is configurable via the smtpd_tls_finger-
       print_digest parameter (hard-coded as  md5  prior  to  Postfix  version
       2.5).

       Postfix  lookup tables are in the form of (key, value) pairs.  Since we
       only need the key, the value can be chosen freely, e.g.   the  name  of
       the   user   or  host:  D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80
       lutzpc.at.home

       Example:

       relay_clientcerts = hash:/etc/postfix/relay_clientcerts

       For more fine-grained control, use check_ccert_access to select an  ap-
       propriate   access(5)   policy   for   each   client.    See   RESTRIC-
       TION_CLASS_README.

       Note: Postfix 2.9.0-2.9.5 computed the public  key  fingerprint  incor-
       rectly.  To  use  public-key  fingerprints, upgrade to Postfix 2.9.6 or
       later.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit   (default:   $default_destination_concur-
       rency_limit)
       The  maximal  number of parallel deliveries to the same destination via
       the relay message delivery transport. This limit  is  enforced  by  the
       queue  manager.  The message delivery transport name is the first field
       in the entry in the master.cf file.

       This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit    (default:    $default_destination_recipi-
       ent_limit)
       The  maximal number of recipients per message for the relay message de-
       livery transport. This limit is enforced by the queue manager. The mes-
       sage  delivery  transport  name  is the first field in the entry in the
       master.cf file.

       Setting this parameter to a value of  1  changes  the  meaning  of  re-
       lay_destination_concurrency_limit from concurrency per domain into con-
       currency per recipient.

       This feature is available in Postfix 2.0 and later.

relay_domains (default: Postfix >= 3.0: empty, Postfix < 3.0: $mydestination)
       What destination domains (and subdomains thereof) this system will  re-
       lay mail to. For details about how the relay_domains value is used, see
       the description of the permit_auth_destination and reject_unauth_desti-
       nation SMTP recipient restrictions.

       Domains  that match $relay_domains are delivered with the $relay_trans-
       port mail delivery transport. The SMTP server validates  recipient  ad-
       dresses with $relay_recipient_maps and rejects non-existent recipients.
       See also the relay domains address class  in  the  ADDRESS_CLASS_README
       file.

       Note: Postfix will not automatically forward mail for domains that list
       this  system  as  their  primary  or  backup  MX  host.  See  the  per-
       mit_mx_backup restriction in the postconf(5) manual page.

       Specify  a  list  of  host  or  domain  names, "/file/name" patterns or
       "type:table" lookup tables,  separated  by  commas  and/or  whitespace.
       Continue  long  lines  by  starting  the  next  line with whitespace. A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table  is matched when a (parent) domain appears as lookup key. Specify
       "!pattern" to exclude a domain from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       Pattern  matching  of domain names is controlled by the presence or ab-
       sence of "relay_domains" in the parent_domain_matches_subdomains param-
       eter value.

relay_domains_reject_code (default: 554)
       The  numerical  Postfix SMTP server response code when a client request
       is rejected by the reject_unauth_destination recipient restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

relay_recipient_maps (default: empty)
       Optional  lookup  tables  with  all valid addresses in the domains that
       match $relay_domains. Specify @domain as a wild-card for  domains  that
       have  no valid recipient list, and become a source of backscatter mail:
       Postfix accepts spam for non-existent recipients and then floods  inno-
       cent  people  with undeliverable mail.  Technically, tables listed with
       $relay_recipient_maps are used as lists: Postfix needs to know only  if
       a  lookup  string  is found or not, but it does not use the result from
       table lookup.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       If this parameter is non-empty, then the Postfix SMTP server  will  re-
       ject mail to unknown relay users. This feature is off by default.

       See  also  the  relay domains address class in the ADDRESS_CLASS_README
       file.

       Example:

       relay_recipient_maps = hash:/etc/postfix/relay_recipients

       This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
       The default mail delivery transport and next-hop destination for remote
       delivery  to domains listed with $relay_domains. In order of decreasing
       precedence, the nexthop destination  is  taken  from  $relay_transport,
       $sender_dependent_relayhost_maps, $relayhost, or from the recipient do-
       main. This information can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of  a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       See  also  the  relay domains address class in the ADDRESS_CLASS_README
       file.

       This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
       The next-hop destination of non-local mail; overrides non-local domains
       in recipient addresses. This information is overruled with relay_trans-
       port,    sender_dependent_default_transport_maps,    default_transport,
       sender_dependent_relayhost_maps and with the transport(5) table.

       On  an intranet, specify the organizational domain name. If your inter-
       nal DNS uses no MX records, specify the name of  the  intranet  gateway
       host instead.

       In  the  case  of SMTP, specify a domain name, hostname, hostname:port,
       [hostname]:port, [hostaddress] or [hostaddress]:port. The  form  [host-
       name] turns off MX lookups.

       If  you're  connected via UUCP, see the UUCP_README file for useful in-
       formation.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.example.com]
       relayhost = uucphost
       relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
       Optional lookup tables with new contact information for  users  or  do-
       mains  that  no  longer  exist.  The table format and lookups are docu-
       mented in relocated(5).

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       If you use this feature, run "postmap /etc/postfix/relocated" to  build
       the  necessary  DBM  or  DB file after change, then "postfix reload" to
       make the changes visible.

       Examples:

       relocated_maps = dbm:/etc/postfix/relocated
       relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)
       Don't rewrite message headers from remote clients at all when this  pa-
       rameter  is  empty;  otherwise,  rewrite message headers and append the
       specified domain name to incomplete  addresses.   The  local_header_re-
       write_clients parameter controls what clients Postfix considers local.

       Examples:

       The  safe  setting:  append  "domain.invalid"  to incomplete header ad-
       dresses from remote SMTP clients, so that  those  addresses  cannot  be
       confused with local addresses.

           remote_header_rewrite_domain = domain.invalid

       The default, purist, setting: don't rewrite headers from remote clients
       at all.

           remote_header_rewrite_domain =

require_home_directory (default: no)
       Require that a local(8) recipient's home directory exists  before  mail
       delivery  is  attempted.  By  default this test is disabled.  It can be
       useful for environments that import home directories to the mail server
       (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).

reset_owner_alias (default: no)
       Reset  the local(8) delivery agent's idea of the owner-alias attribute,
       when delivering mail to a child alias that does not have its own  owner
       alias.

       This  feature is available in Postfix 2.8 and later. With older Postfix
       releases, the behavior is as if this parameter is set to "yes".

       As documented in aliases(5), when an alias name has a  companion  alias
       named  owner-name,  this  will  replace the envelope sender address, so
       that delivery errors will be reported to the owner alias instead of the
       sender. This configuration is recommended for mailing lists.

       A less known property of the owner alias is that it also forces the lo-
       cal(8) delivery agent to write local and remote  addresses  from  alias
       expansion to a new queue file, instead of attempting to deliver mail to
       local addresses as soon as they come out of alias expansion.

       Writing local addresses from alias expansion to a new queue file allows
       for robust handling of temporary delivery errors: errors with one local
       member have no effect on deliveries to other members of the  list.   On
       the other hand, delivery to local addresses as soon as they come out of
       alias expansion is fragile: a temporary error with  one  local  address
       from alias expansion will cause the entire alias to be expanded repeat-
       edly until the error goes away, or until the  message  expires  in  the
       queue.   In that case, a problem with one list member results in multi-
       ple message deliveries to other list members.

       The  default  behavior  of  Postfix  2.8  and  later  is  to  keep  the
       owner-alias  attribute  of  the parent alias, when delivering mail to a
       child alias that does not have its own owner  alias.  Then,  local  ad-
       dresses  from that child alias will be written to a new queue file, and
       a temporary error with one local address will not  affect  delivery  to
       other mailing list members.

       Unfortunately,  older  Postfix releases reset the owner-alias attribute
       when delivering mail to a child alias that does not have its own  owner
       alias.  To  be  precise,  this resets only the decision to create a new
       queue file, not the decision to override the envelope  sender  address.
       The local(8) delivery agent then attempts to deliver local addresses as
       soon as they come out of child alias expansion.  If delivery to any ad-
       dress  from  child  alias expansion fails with a temporary error condi-
       tion, the entire mailing list may be expanded repeatedly until the mail
       expires in the queue, resulting in multiple deliveries of the same mes-
       sage to mailing list members.

resolve_dequoted_address (default: yes)
       Resolve a recipient address safely instead of correctly, by looking in-
       side quotes.

       By default, the Postfix address resolver does not quote the address lo-
       calpart as per RFC 822, so that additional @ or % or !   operators  re-
       main  visible.  This behavior is safe but it is also technically incor-
       rect.

       If you specify "resolve_dequoted_address = no", then  the  Postfix  re-
       solver  will  not know about additional @ etc. operators in the address
       localpart. This opens opportunities for obscure mail relay attacks with
       user@domain@domain  addresses  when  Postfix provides backup MX service
       for Sendmail systems.

resolve_null_domain (default: no)
       Resolve an address that ends in the "@" null domain  as  if  the  local
       hostname were specified, instead of rejecting the address as invalid.

       This  feature  is available in Postfix 2.1 and later.  Earlier versions
       always resolve the null domain as the local hostname.

       The Postfix SMTP server uses this feature to reject mail from or to ad-
       dresses  that  end  in the "@" null domain, and from addresses that re-
       write into a form that ends in the "@" null domain.

resolve_numeric_domain (default: no)
       Resolve "user@ipaddress" as "user@[ipaddress]",  instead  of  rejecting
       the address as invalid.

       This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
       The  name  of  the address rewriting service. This service rewrites ad-
       dresses to standard form and  resolves  them  to  a  (delivery  method,
       next-hop host, recipient) triple.

       This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)
       The  name  of  the  directory with example Postfix configuration files.
       Starting with Postfix 2.1, these files  have  been  replaced  with  the
       postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)
       When  authenticating  to  a remote SMTP or LMTP server with the default
       setting "no", send no SASL authoriZation ID (authzid);  send  only  the
       SASL authentiCation ID (authcid) plus the authcid's password.

       The  non-default  setting  "yes"  enables the behavior of older Postfix
       versions.  These always send a SASL authzid that is equal to  the  SASL
       authcid,  but  this  causes  interoperability  problems  with some SMTP
       servers.

       This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)
       This parameter should not be used. It  was  replaced  by  sender_depen-
       dent_relayhost_maps in Postfix version 2.3.

sender_bcc_maps (default: empty)
       Optional  BCC  (blind  carbon-copy)  address  lookup tables, indexed by
       sender address.  The BCC address (multiple results are  not  supported)
       is added when mail enters from outside of Postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       The table search order is as follows:

       o      Look  up  the  "user+extension@domain.tld" address including the
              optional address extension.

       o      Look up the "user@domain.tld" address without the  optional  ad-
              dress extension.

       o      Look  up the "user+extension" address local part when the sender
              domain equals  $myorigin,  $mydestination,  $inet_interfaces  or
              $proxy_interfaces.

       o      Look  up  the  "user"  address local part when the sender domain
              equals $myorigin, $mydestination, $inet_interfaces or $proxy_in-
              terfaces.

       o      Look up the "@domain.tld" part.

       Note:  with Postfix 2.3 and later the BCC address is added as if it was
       specified with NOTIFY=NONE. The sender will not be  notified  when  the
       BCC  address  is undeliverable, as long as all down-stream software im-
       plements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will be notified when the
       BCC address is undeliverable.

       Note:  automatic  BCC  recipients  are  produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are  not  generated  after
       Postfix  forwards  mail internally, or after Postfix generates mail it-
       self.

       Example:

       sender_bcc_maps = hash:/etc/postfix/sender_bcc

       After a change, run "postmap /etc/postfix/sender_bcc".

       This feature is available in Postfix 2.1 and later.

sender_canonical_classes (default: envelope_sender, header_sender)
       What addresses are subject to  sender_canonical_maps  address  mapping.
       By  default,  sender_canonical_maps address mapping is applied to enve-
       lope sender addresses, and to header sender addresses.

       Specify one or more of: envelope_sender, header_sender

       This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
       Optional address mapping lookup tables for envelope and  header  sender
       addresses.   The  table  format  and  lookups are documented in canoni-
       cal(5).

       Example: you want to rewrite the SENDER address  "user@ugly.domain"  to
       "user@pretty.domain", while still being able to send mail to the RECIP-
       IENT address "user@ugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_default_transport_maps (default: empty)
       A sender-dependent override for the global default_transport  parameter
       setting.  The  tables  are  searched by the envelope sender address and
       @domain. A lookup result of DUNNO terminates the search  without  over-
       riding  the  global default_transport parameter setting.  This informa-
       tion is overruled with the transport(5) table.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       Note: this overrides default_transport, not transport_maps, and  there-
       fore  the  expected syntax is that of default_transport, not the syntax
       of transport_maps.  Specifically, this  does  not  support  the  trans-
       port_maps  syntax  for  null transport, null nexthop, or null email ad-
       dresses.

       For safety reasons, this feature does not allow  $number  substitutions
       in regular expression maps.

       This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)
       A sender-dependent override for the global relayhost parameter setting.
       The tables are searched by the envelope sender address and  @domain.  A
       lookup  result  of  DUNNO  terminates the search without overriding the
       global relayhost parameter setting (Postfix 2.6 and later). This infor-
       mation   is   overruled   with   relay_transport,  sender_dependent_de-
       fault_transport_maps, default_transport and with the  transport(5)  ta-
       ble.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       For  safety  reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

sendmail_fix_line_endings (default: always)
       Controls how the Postfix sendmail command converts email  message  line
       endings from <CR><LF> into UNIX format (<LF>).

       always Always convert message lines ending in <CR><LF>. This setting is
              the default with Postfix 2.9 and later.

       strict Convert message lines ending in <CR><LF> only if the first input
              line ends in <CR><LF>. This setting is backwards-compatible with
              Postfix 2.8 and earlier.

       never  Never convert message lines ending in <CR><LF>. This setting ex-
              ists for completeness only.

       This feature is available in Postfix 2.9 and later.

sendmail_path (default: see postconf -d output)
       A  Sendmail  compatibility  feature  that specifies the location of the
       Postfix sendmail(1) command. This command can be used  to  submit  mail
       into the Postfix queue.

service_name (read-only)
       The  master.cf  service  name  of a Postfix daemon process. This can be
       used to distinguish the logging from different services  that  use  the
       same program name.

       Example master.cf entries:

       # Distinguish inbound MTA logging from submission and smtps logging.
       smtp      inet  n       -       n       -       -       smtpd
       submission inet n       -       n       -       -       smtpd
           -o syslog_name=postfix/$service_name
       smtps     inet  n       -       n       -       -       smtpd
           -o syslog_name=postfix/$service_name

       # Distinguish outbound MTA logging from inbound relay logging.
       smtp      unix  -       -       n       -       -       smtp
       relay     unix  -       -       n       -       -       smtp
           -o syslog_name=postfix/$service_name

service_throttle_time (default: 60s)
       How  long  the Postfix master(8) waits before forking a server that ap-
       pears to be malfunctioning.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

setgid_group (default: postdrop)
       The  group  ownership of set-gid Postfix commands and of group-writable
       Postfix directories. When this parameter value is changed you  need  to
       re-run "postfix set-permissions" (with Postfix version 2.0 and earlier:
       "/etc/postfix/post-install set-permissions".

shlib_directory (default: see 'postconf -d' output)
       The location of Postfix dynamically-linked libraries (libpostfix-*.so),
       and  the  default  location  of Postfix database plugins (postfix-*.so)
       that  have  a  relative  pathname  in  the  dynamicmaps.cf  file.   The
       shlib_directory   parameter  defaults  to  "no"  when  Postfix  dynami-
       cally-linked libraries and database plugins  are  disabled  at  compile
       time,  otherwise  it typically defaults to /usr/lib/postfix or /usr/lo-
       cal/lib/postfix.

       Notes:

       o      The directory specified with shlib_directory should contain only
              Postfix-related  files. Postfix dynamically-linked libraries and
              database plugins should not be installed in  a  "public"  system
              directory  such  as  /usr/lib or /usr/local/lib. Linking Postfix
              dynamically-linked  library  files  or  database  plugins   into
              non-Postfix   programs   is   not  supported.   Postfix  dynami-
              cally-linked libraries and database plugins  implement  a  Post-
              fix-internal API that changes without maintaining compatibility.

       o      You can change the shlib_directory value after Postfix is built.
              However, you may have to run ldconfig or equivalent  to  prevent
              Postfix  programs from failing because the libpostfix-*.so files
              are not found.  No ldconfig command is needed if  you  keep  the
              libpostfix-*.so  files  in the compiled-in default $shlib_direc-
              tory location.

       This feature is available in Postfix 3.0 and later.

show_user_unknown_table_name (default: yes)
       Display the name of the recipient  table  in  the  "User  unknown"  re-
       sponses.   The  extra  detail makes troubleshooting easier but also re-
       veals information that is nobody else's business.

       This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
       The name of the showq(8) service. This service produces mail queue sta-
       tus reports.

       This feature is available in Postfix 2.0 and later.

smtp_address_preference (default: any)
       The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client
       will try first, when a destination has IPv6  and  IPv4  addresses  with
       equal  MX preference. This feature has no effect unless the inet_proto-
       cols setting enables both IPv4 and IPv6.

       Postfix SMTP client address preference has evolved.  With  Postfix  2.8
       the default is "ipv6"; earlier implementations are hard-coded to prefer
       IPv6 over IPv4.

       Notes for mail delivery between sites that have both IPv4 and IPv6 con-
       nectivity:

       o      The  setting "smtp_address_preference = ipv6" is unsafe.  It can
              fail to deliver mail when there is an outage that affects  IPv6,
              while the destination is still reachable over IPv4.

       o      The  setting "smtp_address_preference = any" is safe. With this,
              mail will eventually be delivered even if  there  is  an  outage
              that affects IPv6 or IPv4, as long as it does not affect both.

       This feature is available in Postfix 2.8 and later.

smtp_address_verify_target (default: rcpt)
       In  the  context of email address verification, the SMTP protocol stage
       that determines whether an email address is deliverable.   Specify  one
       of  "rcpt"  or  "data".   The latter is needed with remote SMTP servers
       that reject recipients after the DATA command.  Use  transport_maps  to
       apply this feature selectively:

           /etc/postfix/main.cf:
               transport_maps = hash:/etc/postfix/transport

           /etc/postfix/transport:
               smtp-domain-that-verifies-after-data    smtp-data-target:
               lmtp-domain-that-verifies-after-data    lmtp-data-target:

           /etc/postfix/master.cf:
               smtp-data-target    unix    -    -    n    -    -    smtp
                   -o smtp_address_verify_target=data
               lmtp-data-target    unix    -    -    n    -    -    lmtp
                   -o lmtp_address_verify_target=data

       Unselective  use  of the "data" target does no harm, but will result in
       unnecessary "lost connection after DATA"  events  at  remote  SMTP/LMTP
       servers.

       This feature is available in Postfix 3.0 and later.

smtp_always_send_ehlo (default: yes)
       Always send EHLO at the start of an SMTP session.

       With  "smtp_always_send_ehlo  = no", the Postfix SMTP client sends EHLO
       only when the word "ESMTP" appears in the server greeting banner (exam-
       ple: 220 spike.porcupine.org ESMTP Postfix).

smtp_balance_inet_protocols (default: yes)
       When  a  remote  destination resolves to a combination of IPv4 and IPv6
       addresses, ensure that the Postfix SMTP client  can  try  both  address
       types before it runs into the smtp_mx_address_limit.

       This  avoids an interoperability problem when a destination resolves to
       primarily IPv6 addresses,  the  smtp_address_limit  feature  eliminates
       most  or  all IPv4 addresses, and the destination is not reachable over
       IPv6.

       This feature is available in Postfix 3.3 and later.

smtp_bind_address (default: empty)
       An optional numerical network address  that  the  Postfix  SMTP  client
       should bind to when making an IPv4 connection.

       This  can  be specified in the main.cf file for all SMTP clients, or it
       can be specified in the master.cf file for a specific client, for exam-
       ple:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address=11.22.33.44

       Note  1:  when inet_interfaces specifies no more than one IPv4 address,
       and that address is a non-loopback address, it is automatically used as
       the  smtp_bind_address.  This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

smtp_bind_address6 (default: empty)
       An optional numerical network address  that  the  Postfix  SMTP  client
       should bind to when making an IPv6 connection.

       This feature is available in Postfix 2.2 and later.

       This  can  be specified in the main.cf file for all SMTP clients, or it
       can be specified in the master.cf file for a specific client, for exam-
       ple:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

       Note  1:  when inet_interfaces specifies no more than one IPv6 address,
       and that address is a non-loopback address, it is automatically used as
       the smtp_bind_address6.  This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not recommended here.

smtp_body_checks (default: empty)
       Restricted body_checks(5) tables for the Postfix  SMTP  client.   These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)
       When the remote SMTP servername is a DNS CNAME, replace the  servername
       with  the  result from CNAME expansion for the purpose of logging, SASL
       password lookup, TLS policy decisions, or TLS certificate verification.
       The  value  "no" hardens Postfix smtp_tls_per_site hostname-based poli-
       cies against false hostname information in DNS CNAME records, and makes
       SASL  password  file lookups more predictable. This is the default set-
       ting as of Postfix 2.3.

       When  DNS  CNAME  records  are  validated  with  secure   DNS   lookups
       (smtp_dns_support_level  = dnssec), they are always allowed to override
       the above servername (Postfix 2.11 and later).

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
       The Postfix SMTP client time limit for completing a TCP connection,  or
       zero (use the operating system built-in time limit).

       When  no  connection  can be made within the deadline, the Postfix SMTP
       client tries the next address on the mail exchanger list. Specify 0  to
       disable the time limit (i.e. use whatever timeout is implemented by the
       operating system).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_connection_cache_destinations (default: empty)
       Permanently  enable  SMTP connection caching for the specified destina-
       tions.  With SMTP connection caching, a connection is not closed  imme-
       diately  after  completion of a mail transaction.  Instead, the connec-
       tion is kept open for up to $smtp_connection_cache_time_limit  seconds.
       This  allows connections to be reused for other deliveries, and can im-
       prove mail delivery performance.

       Specify a comma or  white  space  separated  list  of  destinations  or
       pseudo-destinations:

       o      if  mail  is  sent  without  a  relay  host:  a domain name (the
              right-hand side of an email address, without the [] around a nu-
              meric IP address),

       o      if  mail is sent via a relay host: a relay host name (without []
              or non-default TCP port), as specified  in  main.cf  or  in  the
              transport map,

       o      if  mail  is  sent via a UNIX-domain socket: a pathname (without
              the unix: prefix),

       o      a /file/name with domain names and/or relay host  names  as  de-
              fined above,

       o      a  "type:table" with domain names and/or relay host names on the
              left-hand side.  The right-hand side  result  from  "type:table"
              lookups is ignored.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
       Temporarily  enable  SMTP  connection caching while a destination has a
       high volume of mail in the active queue.  With SMTP connection caching,
       a  connection  is  not  closed  immediately  after completion of a mail
       transaction.  Instead, the connection is kept open for up to $smtp_con-
       nection_cache_time_limit seconds.  This allows connections to be reused
       for other deliveries, and can improve mail delivery performance.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_time_limit (default: 2s)
       When SMTP connection caching is enabled, the amount of time that an un-
       used SMTP client socket is kept open before it is closed.  Do not spec-
       ify larger values without permission from the remote sites.

       This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_count_limit (default: 0)
       When SMTP connection caching is enabled, the number of  times  that  an
       SMTP  session  may  be  reused before it is closed, or zero (no limit).
       With a reuse count limit of N, a connection is used up to N+1 times.

       NOTE: This feature is unsafe. When a high-volume destination has multi-
       ple  inbound  MTAs,  then the slowest inbound MTA will attract the most
       connections to that destination.  This limitation does not  exist  with
       the smtp_connection_reuse_time_limit feature.

       This feature is available in Postfix 2.11.

smtp_connection_reuse_time_limit (default: 300s)
       The amount of time during which Postfix will use an SMTP connection re-
       peatedly.  The timer starts when the connection is initiated  (i.e.  it
       includes the connect, greeting and helo latency, in addition to the la-
       tencies of subsequent mail delivery transactions).

       This feature addresses a performance stability problem with remote SMTP
       servers.  This  problem  is not specific to Postfix: it can happen when
       any MTA sends large amounts of SMTP email to a site that  has  multiple
       MX hosts.

       The  problem  starts  when one of a set of MX hosts becomes slower than
       the rest.  Even though SMTP clients connect to fast and slow  MX  hosts
       with equal probability, the slow MX host ends up with more simultaneous
       inbound connections than the faster MX hosts, because the slow MX  host
       needs more time to serve each client request.

       The  slow  MX  host becomes a connection attractor.  If one MX host be-
       comes N times slower than the rest, it dominates mail delivery  latency
       unless  there  are more than N fast MX hosts to counter the effect. And
       if the number of MX hosts is smaller than N, the mail delivery  latency
       becomes  effectively  that  of the slowest MX host divided by the total
       number of MX hosts.

       The solution uses connection caching in a way that differs from Postfix
       version  2.2.  By limiting the amount of time during which a connection
       can be used repeatedly (instead of limiting the  number  of  deliveries
       over  that  connection), Postfix not only restores fairness in the dis-
       tribution of simultaneous connections across a set of MX hosts, it also
       favors  deliveries over connections that perform well, which is exactly
       what we want.

       The default reuse time limit, 300s, is comparable to the  various  smtp
       transaction timeouts which are fair estimates of maximum excess latency
       for a slow delivery.  Note that hosts may accept thousands of  messages
       over  a  single  connection  within  the  default connection reuse time
       limit. This number is much larger than the default Postfix version  2.2
       limit  of  10 messages per cached connection. It may prove necessary to
       lower the limit to avoid interoperability issues with MTAs that exhibit
       bugs when many messages are delivered via a single connection.  A lower
       reuse time limit risks losing the benefit of connection reuse when  the
       average  connection  and  mail  delivery latency exceeds the reuse time
       limit.

       This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
       The Postfix SMTP client time limit for sending the SMTP  ".",  and  for
       receiving the remote SMTP server response.

       When  no  response is received within the deadline, a warning is logged
       that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_data_init_timeout (default: 120s)
       The  Postfix  SMTP client time limit for sending the SMTP DATA command,
       and for receiving the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)
       The  Postfix  SMTP  client time limit for sending the SMTP message con-
       tent.   When  the  connection  makes  no   progress   for   more   than
       $smtp_data_xfer_timeout  seconds the Postfix SMTP client terminates the
       transfer.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)
       Defer mail delivery when no MX record resolves to an IP address.

       The  default  (no)  is  to return the mail as undeliverable. With older
       Postfix versions the default was to keep trying to deliver the mail un-
       til someone fixed the MX record or until the mail was too old.

       Note:  the  Postfix SMTP client always ignores MX records with equal or
       worse preference than the local MTA itself.

       This feature is available in Postfix 2.1 and later.

smtp_delivery_status_filter (default: $default_delivery_status_filter)
       Optional filter for the smtp(8) delivery agent to change  the  delivery
       status  code or explanatory text of successful or unsuccessful deliver-
       ies.  See default_delivery_status_filter for details.

       NOTE: This feature modifies Postfix SMTP client error or non-error mes-
       sages that may or may not be derived from remote SMTP server responses.
       In contrast, the smtp_reply_filter feature modifies remote SMTP  server
       responses only.

smtp_destination_concurrency_limit    (default:   $default_destination_concur-
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  smtp  message  delivery  transport.  This limit is enforced by the
       queue manager. The message delivery transport name is the  first  field
       in the entry in the master.cf file.

smtp_destination_recipient_limit     (default:    $default_destination_recipi-
       ent_limit)
       The maximal number of recipients per message for the smtp  message  de-
       livery transport. This limit is enforced by the queue manager. The mes-
       sage delivery transport name is the first field in  the  entry  in  the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of smtp_des-
       tination_concurrency_limit from concurrency per domain into concurrency
       per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with case in-
       sensitive lists of EHLO keywords  (pipelining,  starttls,  auth,  etc.)
       that  the  Postfix  SMTP client will ignore in the EHLO response from a
       remote SMTP server. See smtp_discard_ehlo_keywords for details. The ta-
       ble  is  not  indexed  by  hostname  for  consistency  with  smtpd_dis-
       card_ehlo_keyword_address_maps.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining,  starttls,  auth,
       etc.)  that  the  Postfix  SMTP client will ignore in the EHLO response
       from a remote SMTP server.

       This feature is available in Postfix 2.2 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

       o      Use  the  smtp_discard_ehlo_keyword_address_maps feature to dis-
              card EHLO keywords selectively.

smtp_dns_reply_filter (default: empty)
       Optional filter for Postfix SMTP client DNS  lookup  results.   Specify
       zero  or  more  lookup  tables.   The lookup tables are searched in the
       given order for a match with the DNS lookup result,  converted  to  the
       following form:

           name ttl class type preference value

       The class field is always "IN", the preference field exists only for MX
       records, the names of hosts, domains, etc.  end in ".", and those names
       are in ASCII form (xn--mumble form in the case of UTF8 names).

       When a match is found, the table lookup result specifies an action.  By
       default, the table query and  the  action  name  are  case-insensitive.
       Currently, only the IGNORE action is implemented.

       Notes:

       o      Postfix DNS reply filters have no effect on implicit DNS lookups
              through nsswitch.conf or equivalent mechanisms.

       o      The Postfix  SMTP/LMTP  client  uses  smtp_dns_reply_filter  and
              lmtp_dns_reply_filter  only  to  discover  a remote SMTP or LMTP
              service (record types MX, A, AAAAA, and  TLSA).   These  lookups
              are also made to implement the features reject_unverified_sender
              and reject_unverified_recipient.

       o      The Postfix SMTP/LMTP client defers mail delivery when a  filter
              removes all lookup results from a successful query.

       o      Postfix  SMTP server uses smtpd_dns_reply_filter only to look up
              MX, A, AAAAA, and TXT records  to  implement  the  features  re-
              ject_unknown_helo_hostname,   reject_unknown_sender_domain,  re-
              ject_unknown_recipient_domain, reject_rbl_*, and reject_rhsbl_*.

       o      The Postfix SMTP server logs a warning or defers  mail  delivery
              when  a  filter  removes  all  lookup  results from a successful
              query.

       Example: ignore Google AAAA records in Postfix SMTP client DNS lookups,
       because Google sometimes hard-rejects mail from IPv6 clients with valid
       PTR etc. records.

       /etc/postfix/main.cf:
           smtp_dns_reply_filter = pcre:/etc/postfix/smtp_dns_reply_filter

       /etc/postfix/smtp_dns_reply_filter:
           # /domain ttl IN AAAA address/ action, all case-insensitive.
           # Note: the domain name ends in ".".
           /^\S+\.google\.com\.\s+\S+\s+\S+\s+AAAA\s+/ IGNORE

       This feature is available in Postfix 3.0 and later.

smtp_dns_resolver_options (default: empty)
       DNS Resolver options for the Postfix SMTP client.  Specify zero or more
       of  the  following  options,  separated by comma or whitespace.  Option
       names are case-sensitive. Some options refer to domain names  that  are
       specified in the file /etc/resolv.conf or equivalent.

       res_defnames
              Append  the current domain name to single-component names (those
              that do not contain a "." character). This can produce incorrect
              results, and is the hard-coded behavior prior to Postfix 2.8.

       res_dnsrch
              Search  for  host  names in the current domain and in parent do-
              mains. This can produce incorrect results and is  therefore  not
              recommended.

       This feature is available in Postfix 2.8 and later.

smtp_dns_support_level (default: empty)
       Level  of  DNS support in the Postfix SMTP client.  With "smtp_dns_sup-
       port_level"  left  at  its  empty  default  value,  the  legacy   "dis-
       able_dns_lookups"  parameter  controls  whether  DNS  is enabled in the
       Postfix SMTP client, otherwise the legacy parameter is ignored.

       Specify one of the following:

       disabled
              Disable DNS lookups.  No MX lookups are performed  and  hostname
              to  address  lookups are unconditionally "native".  This setting
              is not appropriate for hosts that deliver mail to the public In-
              ternet.   Some obsolete how-to documents recommend disabling DNS
              lookups in some configurations with content_filters.  This is no
              longer required and strongly discouraged.

       enabled
              Enable DNS lookups.  Nexthop destination domains not enclosed in
              "[]" will be subject to MX lookups.  If "dns" and  "native"  are
              included  in the "smtp_host_lookup" parameter value, DNS will be
              queried first to resolve MX-host A records, followed by "native"
              lookups if no answer is found in DNS.

       dnssec Enable  DNSSEC  lookups.   The "dnssec" setting differs from the
              "enabled" setting above in the following ways:

       o      Any MX lookups will set RES_USE_DNSSEC and RES_USE_EDNS0 to  re-
              quest   DNSSEC-validated   responses.  If  the  MX  response  is
              DNSSEC-validated the corresponding hostnames are considered val-
              idated.

       o      The  address  lookups of validated hostnames are also validated,
              (provided of course "smtp_host_lookup" includes "dns",  see  be-
              low).

       o      Temporary failures in DNSSEC-enabled hostname-to-address resolu-
              tion block any "native" lookups.   Additional  "native"  lookups
              only happen when DNSSEC lookups hard-fail (NODATA or NXDOMAIN).

       The  Postfix  SMTP  client  considers  non-MX  "[nexthop]"  and  "[nex-
       thop]:port" destinations equivalent to statically-validated MX  records
       of the form "nexthop.  IN MX 0 nexthop."  Therefore, with "dnssec" sup-
       port turned on, validated hostname-to-address lookups apply to the nex-
       thop  domain  of any "[nexthop]" or "[nexthop]:port" destination.  This
       is also true for LMTP "inet:host" and "inet:host:port" destinations, as
       LMTP hostnames are never subject to MX lookups.

       The "dnssec" setting is recommended only if you plan to use the dane or
       dane-only TLS security level,  otherwise  enabling  DNSSEC  support  in
       Postfix  offers  no additional security.  Postfix DNSSEC support relies
       on an upstream recursive nameserver that validates  DNSSEC  signatures.
       Such  a  DNS  server  will always filter out forged DNS responses, even
       when Postfix itself is not configured to use DNSSEC.

       When using Postfix DANE support the "smtp_host_lookup" parameter should
       include "dns", as DANE is not applicable to hosts resolved via "native"
       lookups.

       As mentioned above, Postfix is not a validating stub resolver;  it  re-
       lies  on the system's configured DNSSEC-validating recursive nameserver
       to perform all DNSSEC validation.  Since this nameserver's DNSSEC-vali-
       dated  responses will be fully trusted, it is strongly recommended that
       the MTA host have a local  DNSSEC-validating  recursive  caching  name-
       server  listening  on a loopback address, and be configured to use only
       this nameserver for all lookups.  Otherwise, Postfix may remain subject
       to  man-in-the-middle  attacks  that forge responses from the recursive
       nameserver

       DNSSEC support requires a version of Postfix compiled against a reason-
       ably-modern  DNS resolver(3) library that implements the RES_USE_DNSSEC
       and RES_USE_EDNS0 resolver options.

       This feature is available in Postfix 2.11 and later.

smtp_enforce_tls (default: no)
       Enforcement mode: require that remote SMTP servers use TLS  encryption,
       and  never  send mail in the clear.  This also requires that the remote
       SMTP server hostname matches the information in the remote server  cer-
       tificate,  and  that the remote SMTP server certificate was issued by a
       CA that is trusted by the  Postfix  SMTP  client.  If  the  certificate
       doesn't  verify or the hostname doesn't match, delivery is deferred and
       mail stays in the queue.

       The server hostname is matched against all names provided  as  dNSNames
       in  the SubjectAlternativeName.  If no dNSNames are specified, the Com-
       monName is checked.  The behavior may be changed with the  smtp_tls_en-
       force_peername option.

       This  option  is  useful  only if you are definitely sure that you will
       only connect to servers that support RFC 2487 _and_ that provide  valid
       server  certificates.   Typical  use is for clients that send all their
       email to a dedicated mailhub.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)
       Optional  list of relay hosts for SMTP destinations that can't be found
       or that are unreachable. With Postfix 2.2 and earlier this parameter is
       called fallback_relay.

       By  default,  mail  is returned to the sender when a destination is not
       found, and delivery is deferred when a destination is unreachable.

       With bulk email deliveries, it can be beneficial to  run  the  fallback
       relay MTA on the same host, so that it can reuse the sender IP address.
       This speeds up deliveries that are delayed by IP-based reputation  sys-
       tems (greylist, etc.).

       The  fallback relays must be SMTP destinations. Specify a domain, host,
       host:port, [host]:port, [address] or [address]:port;  the  form  [host]
       turns off MX lookups.  If you specify multiple SMTP destinations, Post-
       fix will try them in the specified order.

       To prevent mailer loops between MX hosts and fall-back  hosts,  Postfix
       version 2.2 and later will not use the fallback relays for destinations
       that it is MX host for (assuming DNS lookup is turned on).

smtp_generic_maps (default: empty)
       Optional lookup tables that perform address rewriting  in  the  Postfix
       SMTP  client,  typically  to  transform  a locally valid address into a
       globally valid address when sending mail across the Internet.  This  is
       needed  when  the  local  machine does not have its own Internet domain
       name, but uses something like localdomain.local instead.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       The table format and lookups are documented in generic(5); examples are
       shown in the ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README
       documents.

       This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)
       Restricted header_checks(5) tables for the Postfix SMTP client.   These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)
       The hostname to send in the SMTP HELO or EHLO command.

       The default value is the  machine  hostname.   Specify  a  hostname  or
       [ip.add.re.ss].

       This  information  can  be  specified  in the main.cf file for all SMTP
       clients, or it can be specified in the master.cf file  for  a  specific
       client, for example:

           /etc/postfix/master.cf:
               mysmtp ... smtp -o smtp_helo_name=foo.bar.com

       This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
       The  Postfix  SMTP  client time limit for sending the HELO or EHLO com-
       mand, and for receiving the initial remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_host_lookup (default: dns)
       What mechanisms the Postfix SMTP client uses to look up a host's IP ad-
       dress.  This parameter is ignored when DNS lookups are  disabled  (see:
       disable_dns_lookups  and  smtp_dns_support_level).  The "dns" mechanism
       is always tried before "native" if both are listed.

       Specify one of the following:

       dns    Hosts can be found in the DNS (preferred).

       native Use the native naming service only (nsswitch.conf, or equivalent
              mechanism).

       dns, native
              Use the native service for hosts not found in the DNS.

       This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 998)
       The  maximal  length of message header and body lines that Postfix will
       send via SMTP. This limit does not include the <CR><LF> at the  end  of
       each  line.  Longer lines are broken by inserting "<CR><LF><SPACE>", to
       minimize the damage to MIME formatted mail.

       The Postfix limit of 998 characters not including <CR><LF>  is  consis-
       tent  with  the  SMTP limit of 1000 characters including <CR><LF>.  The
       Postfix limit was 990 with Postfix 2.8 and earlier.

smtp_mail_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the MAIL  FROM  command,
       and for receiving the remote SMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_mime_header_checks (default: empty)
       Restricted mime_header_checks(5) tables for the  Postfix  SMTP  client.
       These  tables are searched while mail is being delivered.  Actions that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)
       The maximal number of MX (mail exchanger) IP addresses that can  result
       from  Postfix  SMTP  client mail exchanger lookups, or zero (no limit).
       Prior to Postfix version 2.3, this limit was disabled by default.

       This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
       The maximal number of SMTP sessions per  delivery  request  before  the
       Postfix  SMTP client gives up or delivers to a fall-back relay host, or
       zero (no limit). This restriction ignores sessions that  fail  to  com-
       plete  the  SMTP initial handshake (Postfix version 2.2 and earlier) or
       that fail to complete the EHLO and TLS handshake (Postfix  version  2.3
       and later).

       This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)
       Restricted  nested_header_checks(5) tables for the Postfix SMTP client.
       These tables are searched while mail is being delivered.  Actions  that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)
       Never  send EHLO at the start of an SMTP session. See also the smtp_al-
       ways_send_ehlo parameter.

smtp_per_record_deadline (default: no)
       Change the behavior of the smtp_*_timeout  time  limits,  from  a  time
       limit per read or write system call, to a time limit to send or receive
       a complete record (an SMTP command line, SMTP response line, SMTP  mes-
       sage  content  line,  or TLS protocol message).  This limits the impact
       from hostile peers that trickle data one byte at a time.

       Note: when per-record deadlines are enabled, a short timeout may  cause
       problems  with TLS over very slow network connections.  The reasons are
       that a TLS protocol message can be up to 16 kbytes long  (with  TLSv1),
       and that an entire TLS protocol message must be sent or received within
       the per-record deadline.

       This feature is available in Postfix 2.9 and later. With older  Postfix
       releases, the behavior is as if this parameter is set to "no".

smtp_pix_workaround_delay_time (default: 10s)
       How  long  the Postfix SMTP client pauses before sending ".<CR><LF>" in
       order to work around the PIX firewall "<CR><LF>.<CR><LF>" bug.

       Choosing a too short time makes this workaround ineffective when  send-
       ing large messages over slow network connections.

smtp_pix_workaround_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with per-des-
       tination workarounds for CISCO PIX firewall bugs.  The table is not in-
       dexed  by  hostname  for consistency with smtp_discard_ehlo_keyword_ad-
       dress_maps.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
       How long a message must be queued before the Postfix SMTP client  turns
       on  the  PIX  firewall  "<CR><LF>.<CR><LF>" bug workaround for delivery
       through firewalls with "smtp fixup" mode turned on.

       By default, the workaround is turned off for mail that  is  queued  for
       less  than  500  seconds.  In  other  words, the workaround is normally
       turned off for the first delivery attempt.

       Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug workaround
       upon the first delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
       A  list  that specifies zero or more workarounds for CISCO PIX firewall
       bugs. These workarounds are implemented by  the  Postfix  SMTP  client.
       Workaround names are separated by comma or space, and are case insensi-
       tive.  This parameter setting can  be  overruled  with  per-destination
       smtp_pix_workaround_maps settings.

       delay_dotcrlf
              Insert  a  delay before sending ".<CR><LF>" after the end of the
              message content.  The delay is  subject  to  the  smtp_pix_work-
              around_delay_time and smtp_pix_workaround_threshold_time parame-
              ter settings.

       disable_esmtp
              Disable all extended SMTP commands: send HELO instead of EHLO.

       This feature is available in Postfix 2.4 and later.  The  default  set-
       tings are backwards compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
       The  Postfix  SMTP  client time limit for sending the QUIT command, and
       for receiving the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)
       Quote  addresses  in Postfix SMTP client MAIL FROM and RCPT TO commands
       as required by RFC 5321. This includes putting quotes around an address
       localpart that ends in ".".

       The  default  is to comply with RFC 5321. If you have to send mail to a
       broken SMTP server, configure a special SMTP client in master.cf:

           /etc/postfix/master.cf:
               broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

       and route mail for the destination in  question  to  the  "broken-smtp"
       message delivery with a transport(5) table.

       This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
       Randomize  the  order of equal-preference MX host addresses.  This is a
       performance feature of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the SMTP  RCPT  TO  com-
       mand, and for receiving the remote SMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_reply_filter (default: empty)
       A mechanism to transform replies from remote SMTP servers one line at a
       time.   This  is  a last-resort tool to work around server replies that
       break interoperability with the Postfix SMTP client.   Other  uses  in-
       volve fault injection to test Postfix's handling of invalid responses.

       Notes:

       o      In  the case of a multi-line reply, the Postfix SMTP client uses
              the final reply line's numerical SMTP reply  code  and  enhanced
              status code.

       o      The  numerical  SMTP  reply code (XYZ) takes precedence over the
              enhanced status code (X.Y.Z).  When  the  enhanced  status  code
              initial digit differs from the SMTP reply code initial digit, or
              when no enhanced status code is present, the Postfix SMTP client
              uses a generic enhanced status code (X.0.0) instead.

       Specify the name of a "type:table" lookup table. The search string is a
       single SMTP reply line as received from the remote SMTP server,  except
       that  the trailing <CR><LF> are removed.  When the lookup succeeds, the
       result replaces the single SMTP reply line.

       Examples:

       /etc/postfix/main.cf:
           smtp_reply_filter = pcre:/etc/postfix/reply_filter

       /etc/postfix/reply_filter:
           # Transform garbage into "250-filler..." so that it looks like
           # one line from a multi-line reply. It does not matter what we
           # substitute here as long it has the right syntax.  The Postfix
           # SMTP client will use the final line's numerical SMTP reply
           # code and enhanced status code.
           !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

       This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)
       The Postfix SMTP client time limit for sending the  RSET  command,  and
       for  receiving  the  remote SMTP server response. The SMTP client sends
       RSET in order to finish a recipient address probe, or to verify that  a
       cached session is still usable.

       This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)
       An optional table to prevent repeated SASL authentication failures with
       the same remote SMTP server hostname, username and password. Each table
       (key,  value) pair contains a server name, a username and password, and
       the full server response. This information is stored when a remote SMTP
       server  rejects  an  authentication  attempt with a 535 reply code.  As
       long as the smtp_sasl_password_maps information does no change, and  as
       long  as the smtp_sasl_auth_cache_name information does not expire (see
       smtp_sasl_auth_cache_time) the Postfix SMTP client avoids SASL  authen-
       tication  attempts with the same server, username and password, and in-
       stead   bounces   or   defers   mail    as    controlled    with    the
       smtp_sasl_auth_soft_bounce configuration parameter.

       Use   a   per-destination  delivery  concurrency  of  1  (for  example,
       "smtp_destination_concurrency_limit  =  1",  "relay_destination_concur-
       rency_limit = 1", etc.), otherwise multiple delivery agents may experi-
       ence a login failure at the same time.

       The table must be accessed via the proxywrite  service,  i.e.  the  map
       name must start with "proxy:". The table should be stored under the di-
       rectory specified with the data_directory parameter.

       This feature uses cryptographic hashing  to  protect  plain-text  pass-
       words, and requires that Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/lib/postfix/sasl_auth_cache

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)
       The  maximal age of an smtp_sasl_auth_cache_name entry before it is re-
       moved.

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP client.  By default, the
       Postfix SMTP client uses no authentication.

       Example:

       smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)
       When  a remote SMTP server rejects a SASL authentication request with a
       535 reply code, defer mail delivery instead of returning mail as  unde-
       liverable.  The latter behavior was hard-coded prior to Postfix version
       2.5.

       Note: the setting "yes" overrides the global soft_bounce parameter, but
       the setting "no" does not.

       Example:

       # Default as of Postfix 2.5
       smtp_sasl_auth_soft_bounce = yes
       # The old hard-coded default
       smtp_sasl_auth_soft_bounce = no

       This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)
       If non-empty, a Postfix SMTP client filter for the remote SMTP server's
       list of offered SASL mechanisms.  Different client and server implemen-
       tations  may support different mechanism lists; by default, the Postfix
       SMTP client will use the  intersection  of  the  two.  smtp_sasl_mecha-
       nism_filter  specifies  an  optional  third mechanism list to intersect
       with.

       Specify mechanism names, "/file/name" patterns or  "type:table"  lookup
       tables.  The  right-hand  side  result from "type:table" lookups is ig-
       nored. Specify "!pattern" to exclude a mechanism name  from  the  list.
       The  form  "!/file/name"  is  supported only in Postfix version 2.4 and
       later.

       This feature is available in Postfix 2.2 and later.

       Examples:

       smtp_sasl_mechanism_filter = plain, login
       smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
       smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
       Optional Postfix SMTP client lookup tables with  one  username:password
       entry per sender, remote hostname or next-hop domain. Per-sender lookup
       is done only when sender-dependent authentication is  enabled.   If  no
       username:password entry is found, then the Postfix SMTP client will not
       attempt to authenticate to the remote host.

       The Postfix SMTP client opens the lookup table before going  to  chroot
       jail, so you can leave the password file in /etc/postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

smtp_sasl_path (default: empty)
       Implementation-specific information that the Postfix SMTP client passes
       through to the  SASL  plug-in  implementation  that  is  selected  with
       smtp_sasl_type.   Typically  this specifies the name of a configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
       Postfix SMTP client SASL security options; as of Postfix 2.3  the  list
       of available features depends on the SASL client implementation that is
       selected with smtp_sasl_type.

       The following security features are defined for the cyrus  client  SASL
       implementation:

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       mutual_auth
              Only  allow  methods  that  provide  mutual  authentication (not
              available with SASL version 1).

       Example:

       smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
       The SASL authentication security options that the Postfix  SMTP  client
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options  (default: $smtp_sasl_tls_security_op-
       tions)
       The SASL authentication security options that the Postfix  SMTP  client
       uses  for  TLS  encrypted SMTP sessions with a verified server certifi-
       cate.

       When mail is sent to the public MX host  for  the  recipient's  domain,
       server certificates are by default optional, and delivery proceeds even
       if certificate verification fails. For delivery via a  submission  ser-
       vice  that  requires SASL authentication, it may be appropriate to send
       plaintext passwords only when the connection to the server is  strongly
       encrypted and the server identity is verified.

       The smtp_sasl_tls_verified_security_options parameter makes it possible
       to only enable plaintext mechanisms when a  secure  connection  to  the
       server is available. Submission servers subject to this policy must ei-
       ther have verifiable certificates or offer suitable non-plaintext  SASL
       mechanisms.

       This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)
       The  SASL  plug-in type that the Postfix SMTP client should use for au-
       thentication.  The available types are listed with  the  "postconf  -A"
       command.

       This feature is available in Postfix 2.3 and later.

smtp_send_dummy_mail_auth (default: no)
       Whether  or not to append the "AUTH=<>" option to the MAIL FROM command
       in SASL-authenticated SMTP sessions. The default is not to  send  this,
       to  avoid problems with broken remote SMTP servers.  Before Postfix 2.9
       the behavior is as if "smtp_send_dummy_mail_auth = yes".

       This feature is available in Postfix 2.9 and later.

smtp_send_xforward_command (default: no)
       Send the non-standard XFORWARD command when  the  Postfix  SMTP  server
       EHLO response announces XFORWARD support.

       This allows a Postfix SMTP delivery agent, used for injecting mail into
       a content filter, to forward the name, address, protocol and HELO  name
       of  the  original  client  to the content filter and downstream queuing
       SMTP  server.  This  can  produce  more  useful  logging  than   local-
       host[127.0.0.1] etc.

       This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
       Enable sender-dependent authentication in the Postfix SMTP client; this
       is available only with SASL authentication, and disables  SMTP  connec-
       tion  caching  to  ensure that mail from different senders will use the
       appropriate credentials.

       This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
       Skip SMTP servers that greet with a 4XX status code (go away, try again
       later).

       By  default,  the Postfix SMTP client moves on the next mail exchanger.
       Specify "smtp_skip_4xx_greeting = no" if Postfix should defer  delivery
       immediately.

       This  feature  is  available in Postfix 2.0 and earlier.  Later Postfix
       versions always skip remote SMTP servers that greet with a  4XX  status
       code.

smtp_skip_5xx_greeting (default: yes)
       Skip remote SMTP servers that greet with a 5XX status code.

       By  default,  the Postfix SMTP client moves on the next mail exchanger.
       Specify "smtp_skip_5xx_greeting = no" if Postfix should bounce the mail
       immediately.  Caution:  the  latter  behavior appears to contradict RFC
       2821.

smtp_skip_quit_response (default: yes)
       Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
       Time limit for Postfix SMTP client write and read operations during TLS
       startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtp_tcp_port (default: smtp)
       The default TCP port that the Postfix SMTP client connects to.  Specify
       a symbolic name (see services(5)) or a numeric port.

smtp_tls_CAfile (default: empty)
       A file containing CA certificates of root CAs trusted  to  sign  either
       remote SMTP server certificates or intermediate CA certificates.  These
       are loaded into memory before the  smtp(8)  client  enters  the  chroot
       jail.  If  the  number  of  trusted  roots  is  large,  consider  using
       smtp_tls_CApath instead, but note that the  latter  directory  must  be
       present in the chroot jail if the smtp(8) client is chrooted. This file
       may also be used to augment the client certificate trust chain, but  it
       is   best   to  include  all  the  required  certificates  directly  in
       $smtp_tls_cert_file (or, Postfix >= 3.4 $smtp_tls_chain_files).

       Specify "smtp_tls_CAfile = /path/to/system_CA_file"  to  use  ONLY  the
       system-supplied default Certification Authority certificates.

       Specify  "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
       Directory with PEM format Certification Authority certificates that the
       Postfix  SMTP  client  uses to verify a remote SMTP server certificate.
       Don't forget to create the necessary "hash" links  with,  for  example,
       "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

       To  use  this option in chroot mode, this directory (or a copy) must be
       inside the chroot jail.

       Specify "smtp_tls_CApath = /path/to/system_CA_directory"  to  use  ONLY
       the system-supplied default Certification Authority certificates.

       Specify  "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)
       Try to detect a mail hijacking attack based on a TLS protocol  vulnera-
       bility  (CVE-2009-3555),  where  an  attacker  prepends malicious HELO,
       MAIL, RCPT, DATA commands to a Postfix SMTP client  TLS  session.   The
       attack  would  succeed  with non-Postfix SMTP servers that reply to the
       malicious HELO, MAIL, RCPT, DATA commands after negotiating the Postfix
       SMTP client TLS session.

       This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)
       File  with the Postfix SMTP client RSA certificate in PEM format.  This
       file may also contain the Postfix SMTP  client  private  RSA  key,  and
       these  may  be  the same as the Postfix SMTP server RSA certificate and
       key file.  With Postfix >= 3.4 the preferred way  to  configure  client
       keys and certificates is via the "smtp_tls_chain_files" parameter.

       Do not configure client certificates unless you must present client TLS
       certificates to one or more servers. Client certificates are  not  usu-
       ally  needed,  and  can cause problems in configurations that work well
       without them. The recommended setting is to let the defaults stand:

           smtp_tls_cert_file =
           smtp_tls_key_file =
           smtp_tls_eccert_file =
           smtp_tls_eckey_file =
           # Obsolete DSA parameters
           smtp_tls_dcert_file =
           smtp_tls_dkey_file =
           # Postfix >= 3.4 interface
           smtp_tls_chain_files =

       The best way to use the default settings is to comment  out  the  above
       parameters in main.cf if present.

       To  enable  remote  SMTP servers to verify the Postfix SMTP client cer-
       tificate, the issuing CA certificates must be  made  available  to  the
       server. You should include the required certificates in the client cer-
       tificate file, the client certificate first,  then  the  issuing  CA(s)
       (bottom-up order).

       Example: the certificate for "client.example.com" was issued by "inter-
       mediate CA" which itself has a certificate issued by "root CA".  As the
       "root" super-user create the client.pem file with:

           # umask 077
           # cat client_key.pem client_cert.pem intermediate_CA.pem > chain.pem

       If  you  also  want to verify remote SMTP server certificates issued by
       these CAs, you can add the CA certificates to the  smtp_tls_CAfile,  in
       which  case it is not necessary to have them in the smtp_tls_cert_file,
       smtp_tls_dcert_file (obsolete) or smtp_tls_eccert_file.

       A certificate supplied here must be usable as an SSL client certificate
       and hence pass the "openssl verify -purpose sslclient ..." test.

       Example:

       smtp_tls_cert_file = /etc/postfix/chain.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_chain_files (default: empty)
       List  of  one  or more PEM files, each holding one or more private keys
       directly followed by a corresponding certificate chain.  The file names
       are  separated  by  commas and/or whitespace.  This parameter obsoletes
       the legacy algorithm-specific key and certificate file settings.   When
       this  parameter  is non-empty, the legacy parameters are ignored, and a
       warning is logged if any are also non-empty.

       With the proliferation of multiple private key algorithms-which, as  of
       OpenSSL 1.1.1, include DSA (obsolete), RSA, ECDSA, Ed25519 and Ed448-it
       is increasingly impractical to use separate parameters to configure the
       key  and  certificate chain for each algorithm.  Therefore, Postfix now
       supports storing multiple keys and corresponding certificate chains  in
       a single file or in a set of files.

       Each  key must appear immediately before the corresponding certificate,
       optionally followed by additional issuer certificates that complete the
       certificate  chain  for  that  key.  When multiple files are specified,
       they are equivalent to a single file that is  concatenated  from  those
       files  in  the  given order.  Thus, while a key must always precede its
       certificate and issuer chain, it can be in a separate file, so long  as
       that  file  is listed immediately before the file that holds the corre-
       sponding certificate chain.  Once all the files are  concatenated,  the
       sequence  of  PEM  objects must be: key1, cert1, [chain1], key2, cert2,
       [chain2], ..., keyN, certN, [chainN].

       Storing the private key in the same file as the corresponding  certifi-
       cate is more reliable.  With the key and certificate in separate files,
       there is a chance that during key rollover a Postfix process might load
       a  private  key  and  certificate from separate files that don't match.
       Various operational errors may even result in a persistent broken  con-
       figuration in which the certificate does not match the private key.

       The  file  or files must contain at most one key of each type.  If, for
       example, two or more RSA keys and corresponding chains are listed,  de-
       pending on the version of OpenSSL either only the last one will be used
       or an configuration error may be detected.  Note that  while  "Ed25519"
       and  "Ed448"  are  considered  separate  algorithms,  the various ECDSA
       curves (typically one of prime256v1, secp384r1 or secp521r1)  are  con-
       sidered as different parameters of a single "ECDSA" algorithm, so it is
       not presently possible to configure keys for more than one ECDSA curve.

       Example (separate files for  each  key  and  corresponding  certificate
       chain):

           /etc/postfix/main.cf:
               smtp_tls_chain_files =
                   ${config_directory}/ed25519.pem,
                   ${config_directory}/ed448.pem,
                   ${config_directory}/rsa.pem

           /etc/postfix/ed25519.pem:
               -----BEGIN PRIVATE KEY-----
               MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
               ...
               nC0egv51YPDWxEHom4QA
               -----END CERTIFICATE-----

           /etc/postfix/ed448.pem:
               -----BEGIN PRIVATE KEY-----
               MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
               LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
               ...
               pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
               -----END CERTIFICATE-----

           /etc/postfix/rsa.pem:
               -----BEGIN PRIVATE KEY-----
               MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
               ...
               ahQkZ3+krcaJvDSMgvu0tDc=
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
               ...
               Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
               -----END CERTIFICATE-----

       Example (all keys and certificates in a single file):

           /etc/postfix/main.cf:
               smtp_tls_chain_files = ${config_directory}/chains.pem

           /etc/postfix/chains.pem:
               -----BEGIN PRIVATE KEY-----
               MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
               ...
               nC0egv51YPDWxEHom4QA
               -----END CERTIFICATE-----
               -----BEGIN PRIVATE KEY-----
               MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
               LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
               ...
               pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
               -----END CERTIFICATE-----
               -----BEGIN PRIVATE KEY-----
               MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
               ...
               ahQkZ3+krcaJvDSMgvu0tDc=
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
               ...
               Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
               -----END CERTIFICATE-----

       This feature is available in Postfix 3.4 and later.

smtp_tls_cipherlist (default: empty)
       Obsolete  Postfix  < 2.3 control for the Postfix SMTP client TLS cipher
       list. As this feature applies to all TLS security levels, it is easy to
       create interoperability problems by choosing a non-default cipher list.
       Do not use a non-default TLS cipher list on hosts that deliver email to
       the  public  Internet: you will be unable to send email to servers that
       only support the ciphers you exclude. Using a  restricted  cipher  list
       may  be  more appropriate for an internal MTA, where one can exert some
       control over the TLS software and settings of the peer servers.

       Note: do not use "" quotes around the parameter value.

       This feature is available in Postfix version 2.2. It is not  used  with
       Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       opportunistic TLS  encryption.  Cipher  types  listed  in  smtp_tls_ex-
       clude_ciphers are excluded from the base definition of the selected ci-
       pher grade.   The default value is "medium" for Postfix releases  after
       the middle of 2015, "export" for older releases.

       When   TLS   is   mandatory   the   cipher  grade  is  chosen  via  the
       smtp_tls_mandatory_ciphers configuration parameter, see there for  syn-
       tax details. See smtp_tls_policy_maps for information on how to config-
       ure ciphers on a per-destination basis.

       This feature is available in Postfix 2.6 and later. With earlier  Post-
       fix  releases  only  the smtp_tls_mandatory_ciphers parameter is imple-
       mented, and opportunistic TLS always uses "export" or better (i.e. all)
       ciphers.

smtp_tls_connection_reuse (default: no)
       Try  to  make  multiple  deliveries per TLS-encrypted connection.  This
       uses the tlsproxy(8) service to encrypt an SMTP  connection,  uses  the
       scache(8) service to save that connection, and relies on hints from the
       qmgr(8) daemon.

       See "Client-side TLS connection reuse" for background details.

       This feature is available in Postfix 3.4 and later.

smtp_tls_dane_insecure_mx_policy (default: dane)
       The TLS policy for MX hosts with "secure" TLSA records when the nexthop
       destination  security level is dane, but the MX record was found via an
       "insecure" MX lookup.  The choices are:

       may    The TLSA records will be ignored and TLS will be  optional.   If
              the MX host does not appear to support STARTTLS, or the STARTTLS
              handshake fails, mail may be sent in the clear.

       encrypt
              The TLSA records will signal a requirement to  use  TLS.   While
              TLS encryption will be required, authentication will not be per-
              formed.

       dane (default)
              The TLSA records will be used just as with "secure" MX  records.
              TLS  encryption  will  be  required, and, if at least one of the
              TLSA records is "usable", authentication will be required.  When
              authentication  succeeds,  it  will be logged only as "Trusted",
              not "Verified", because the MX host name could have been forged.
              Though with "insecure" MX records an active attacker can compro-
              mise  SMTP  transport  security  by returning forged MX records,
              such attacks are "tamper-evident" since any forged MX  hostnames
              will  be  recorded in the mail logs.  Attackers who place a high
              value staying hidden may be deterred from forging MX records.

       This feature is available in Postfix 3.1 and later. The may  policy  is
       backwards-compatible with earlier Postfix versions.

smtp_tls_dcert_file (default: empty)
       File  with the Postfix SMTP client DSA certificate in PEM format.  This
       file may also contain the Postfix SMTP client private DSA key.  The DSA
       algorithm is obsolete and should not be used.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
       File  with the Postfix SMTP client DSA private key in PEM format.  This
       file may be combined with the Postfix SMTP client DSA certificate  file
       specified  with $smtp_tls_dcert_file. The DSA algorithm is obsolete and
       should not be used.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)
       File with the Postfix SMTP client  ECDSA  certificate  in  PEM  format.
       This  file  may also contain the Postfix SMTP client ECDSA private key.
       With Postfix >= 3.4 the preferred way to configure client keys and cer-
       tificates is via the "smtp_tls_chain_files" parameter.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
       File with the Postfix SMTP client ECDSA  private  key  in  PEM  format.
       This  file  may be combined with the Postfix SMTP client ECDSA certifi-
       cate file specified with $smtp_tls_eccert_file.  With  Postfix  >=  3.4
       the  preferred way to configure client keys and certificates is via the
       "smtp_tls_chain_files" parameter.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)
       With  mandatory  TLS  encryption,  require  that the remote SMTP server
       hostname matches the information in the remote SMTP server certificate.
       As  of  RFC 2487 the requirements for hostname checking for MTA clients
       are not specified.

       This option can be set to "no" to disable strict  peer  name  checking.
       This  setting  has  no  effect  on sessions that are controlled via the
       smtp_tls_per_site table.

       Disabling the hostname verification can make sense in  closed  environ-
       ment where special CAs are created.  If not used carefully, this option
       opens the danger of a "man-in-the-middle"  attack  (the  CommonName  of
       this attacker will be logged).

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the Postfix SMTP client
       cipher  list  at  all  TLS  security levels. This is not an OpenSSL ci-
       pherlist, it is a simple list separated by  whitespace  and/or  commas.
       The  elements  are a single cipher, or one or more "+" separated cipher
       properties, in which case only ciphers matching all the properties  are
       excluded.

       Examples (some of these will cause problems):

           smtp_tls_exclude_ciphers = aNULL
           smtp_tls_exclude_ciphers = MD5, DES
           smtp_tls_exclude_ciphers = DES+MD5
           smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtp_tls_exclude_ciphers = kEDH+aRSA

       The  first  setting,  disables anonymous ciphers. The next setting dis-
       ables ciphers that use the MD5 digest algorithm or the (single) DES en-
       cryption  algorithm. The next setting disables ciphers that use MD5 and
       DES together.  The next setting disables the two  ciphers  "AES256-SHA"
       and  "DES-CBC3-MD5".  The  last setting disables ciphers that use "EDH"
       key exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)
       List of acceptable remote SMTP server certificate fingerprints for  the
       "fingerprint"  TLS  security  level  (smtp_tls_security_level = finger-
       print). At this security level, Certification Authorities are not used,
       and  certificate expiration times are ignored. Instead, server certifi-
       cates are verified directly via their certificate fingerprint or public
       key  fingerprint  (Postfix 2.9 and later). The fingerprint is a message
       digest of the server certificate (or public key). The digest  algorithm
       is selected via the smtp_tls_fingerprint_digest parameter.

       When  an  smtp_tls_policy_maps  table entry specifies the "fingerprint"
       security level, any "match" attributes in that entry specify  the  list
       of  valid fingerprints for the corresponding destination. Multiple fin-
       gerprints can be combined with a "|" delimiter in a single match attri-
       bute, or multiple match attributes can be employed.

       Example:  Certificate  fingerprint  verification with internal mailhub.
       Two matching fingerprints are listed. The  relayhost  may  be  multiple
       physical hosts behind a load-balancer, each with its own private/public
       key and self-signed certificate. Alternatively, a single relayhost  may
       be  in  the process of switching from one set of private/public keys to
       another, and both keys are trusted just prior to the transition.

           relayhost = [mailhub.example.com]
           smtp_tls_security_level = fingerprint
           smtp_tls_fingerprint_digest = md5
           smtp_tls_fingerprint_cert_match =
               3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
               EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       Example: Certificate fingerprint verification  with  selected  destina-
       tions.  As in the example above, we show two matching fingerprints:

           /etc/postfix/main.cf:
               smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
               smtp_tls_fingerprint_digest = md5

           /etc/postfix/tls_policy:
               example.com fingerprint
                   match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
                   match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)
       The  message digest algorithm used to construct remote SMTP server cer-
       tificate  fingerprints.  At  the  "fingerprint"  TLS   security   level
       (smtp_tls_security_level = fingerprint), the server certificate is ver-
       ified by directly matching its certificate fingerprint  or  its  public
       key fingerprint (Postfix 2.9 and later). The fingerprint is the message
       digest of the server certificate (or its public key) using the selected
       algorithm.  With a digest algorithm resistant to "second pre-image" at-
       tacks, it is not feasible to create a new public  key  and  a  matching
       certificate (or public/private key-pair) that has the same fingerprint.

       The  default  algorithm  is  md5; this is consistent with the backwards
       compatible setting of the digest used to verify client certificates  in
       the SMTP server.

       The  best practice algorithm is now sha1. Recent advances in hash func-
       tion cryptanalysis have led to md5 being deprecated in favor  of  sha1.
       However,  as  long  as  there  are  no known "second pre-image" attacks
       against md5, its use in this context can still be considered safe.

       While additional digest algorithms are often available  with  OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix. For now this means just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The  text to the right of "=" sign is the desired fingerprint.  For ex-
       ample:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To extract the public key fingerprint from an  X.509  certificate,  you
       need to extract the public key from the certificate and compute the ap-
       propriate digest of its DER (ASN.1) encoding. With OpenSSL  the  "-pub-
       key"  option  of  the  "x509" command extracts the public key always in
       "PEM" format. We pipe the result to another OpenSSL command  that  con-
       verts the key to DER and then to the "dgst" command to compute the fin-
       gerprint.

       The actual command to transform the key to DER format  depends  on  the
       version  of OpenSSL used. With OpenSSL 1.0.0 and later, the "pkey" com-
       mand supports all key types. With OpenSSL 0.9.8 and  earlier,  the  key
       type  is  always  RSA  (nobody uses DSA, and EC keys are not fully sup-
       ported by 0.9.8), so the "rsa" command is used.

           # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl pkey -pubin -outform DER |
               openssl dgst -sha1 -c
           (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

           # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl rsa -pubin -outform DER |
               openssl dgst -md5 -c
           (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fin-
       gerprint  and  public  key  fingerprint  when  the TLS loglevel is 2 or
       higher.

       Note: Postfix 2.9.0-2.9.5 computed the public  key  fingerprint  incor-
       rectly.  To  use  public-key  fingerprints, upgrade to Postfix 2.9.6 or
       later.

       This feature is available in Postfix 2.5 and later.

smtp_tls_force_insecure_host_tlsa_lookup (default: no)
       Lookup the associated DANE TLSA RRset even when a hostname  is  not  an
       alias  and  its  address  records lie in an unsigned zone.  This is un-
       likely to ever yield DNSSEC validated results, since child zones of un-
       signed zones are also unsigned in the absence of DLV or locally config-
       ured non-root trust-anchors.  We anticipate that such  mechanisms  will
       not  be  used for just the "_tcp" subdomain of a host.  Suppressing the
       TLSA RRset lookup reduces latency and avoids potential interoperability
       problems  with  nameservers for unsigned zones that are not prepared to
       handle the new TLSA RRset.

       This feature is available in Postfix 2.11.

smtp_tls_key_file (default: $smtp_tls_cert_file)
       File with the Postfix SMTP client RSA private key in PEM format.   This
       file  may be combined with the Postfix SMTP client RSA certificate file
       specified with $smtp_tls_cert_file.  With Postfix >= 3.4 the  preferred
       way   to   configure   client   keys   and   certificates  is  via  the
       "smtp_tls_chain_files" parameter.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
       Enable additional Postfix SMTP client logging of  TLS  activity.   Each
       logging  level  also includes the information that is logged at a lower
       logging level.

              0 Disable logging of TLS activity.

              1 Log only a summary message on TLS handshake  completion  -  no
              logging  of remote SMTP server certificate trust-chain verifica-
              tion errors if server certificate verification is not  required.
              With Postfix 2.8 and earlier, log the summary message and uncon-
              ditionally log trust-chain verification errors.

              2 Also log levels during TLS negotiation.

              3 Also  log  hexadecimal  and  ASCII  dump  of  TLS  negotiation
              process.

              4  Also  log hexadecimal and ASCII dump of complete transmission
              after STARTTLS.

       Do not use "smtp_tls_loglevel = 2" or higher except in  case  of  prob-
       lems. Use of loglevel 4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       mandatory TLS encryption.  The default value "medium" is  suitable  for
       most destinations with which you may want to enforce TLS, and is beyond
       the reach of today's cryptanalytic  methods.  See  smtp_tls_policy_maps
       for information on how to configure ciphers on a per-destination basis.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or better OpenSSL ciphers.  The underlying
              cipherlist is specified via the tls_export_cipherlist configura-
              tion parameter, which you are strongly encouraged to not change.
              This choice is insecure and SHOULD NOT be used.

       low    Enable "LOW" grade or better OpenSSL  ciphers.   The  underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter, which you are  strongly  encouraged  to  not  change.
              This choice is insecure and SHOULD NOT be used.

       medium Enable "MEDIUM" grade or better OpenSSL ciphers.  The underlying
              cipherlist is specified via the tls_medium_cipherlist configura-
              tion parameter, which you are strongly encouraged to not change.

       high   Enable  only  "HIGH" grade OpenSSL ciphers.  This setting may be
              appropriate when all mandatory TLS destinations (e.g.  when  all
              mail is routed to a suitably capable relayhost) support at least
              one "HIGH" grade cipher. The underlying cipherlist is  specified
              via  the  tls_high_cipherlist configuration parameter, which you
              are strongly encouraged to not change.

       null   Enable only the "NULL" OpenSSL ciphers, these provide  authenti-
              cation  without encryption.  This setting is only appropriate in
              the rare case that all servers are prepared to use NULL  ciphers
              (not  normally  enabled in TLS servers). A plausible use-case is
              an LMTP server listening on a UNIX-domain socket that is config-
              ured  to  support  "NULL"  ciphers. The underlying cipherlist is
              specified via the tls_null_cipherlist  configuration  parameter,
              which you are strongly encouraged to not change.

       The  underlying cipherlists for grades other than "null" include anony-
       mous ciphers, but these are automatically filtered out if  the  Postfix
       SMTP  client is configured to verify server certificates.  You are very
       unlikely to need to take any steps to exclude anonymous  ciphers,  they
       are excluded automatically as necessary.  If you must exclude anonymous
       ciphers at the "may" or "encrypt" security  levels,  when  the  Postfix
       SMTP  client  does not need or use peer certificates, set "smtp_tls_ex-
       clude_ciphers = aNULL". To exclude anonymous ciphers only when  TLS  is
       enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
       Additional  list of ciphers or cipher types to exclude from the Postfix
       SMTP client cipher list at mandatory TLS  security  levels.  This  list
       works  in  addition  to the exclusions listed with smtp_tls_exclude_ci-
       phers (see there for syntax details).

       Starting with Postfix 2.6, the mandatory cipher exclusions can be spec-
       ified  on  a  per-destination basis via the TLS policy "exclude" attri-
       bute. See smtp_tls_policy_maps for notes and examples.

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3)
       List of SSL/TLS protocols that the Postfix SMTP client  will  use  with
       mandatory  TLS  encryption.   In  main.cf  the  values are separated by
       whitespace, commas or colons. In the policy table "protocols" attribute
       (see  smtp_tls_policy_maps) the only valid separator is colon. An empty
       value means allow all protocols. The valid protocol names, (see  \fBfB-
       SSL_get_version(3)),  are  "SSLv2",  "SSLv3"  and  "TLSv1". The default
       value is "!SSLv2, !SSLv3" for Postfix  releases  after  the  middle  of
       2015, "!SSLv2" for older releases.

       With Postfix >= 2.5 the parameter syntax was expanded to support proto-
       col  exclusions.  One  can  explicitly  exclude  "SSLv2"   by   setting
       "smtp_tls_mandatory_protocols  =  !SSLv2".  To exclude both "SSLv2" and
       "SSLv3" set "smtp_tls_mandatory_protocols =  !SSLv2,  !SSLv3".  Listing
       the  protocols  to  include,  rather than protocols to exclude, is sup-
       ported, but not recommended. The exclusion form  more  closely  matches
       the underlying OpenSSL interface semantics.

       The range of protocols advertised by an SSL/TLS client must be contigu-
       ous.  When a protocol version is enabled, disabling any higher  version
       implicitly  disables all versions above that higher version.  Thus, for
       example (assuming the OpenSSL library supports both SSLv2 and SSLv3):

           smtp_tls_mandatory_protocols = !SSLv2, !TLSv1
       also disables any protocols version  higher  than  TLSv1  leaving  only
       "SSLv3" enabled.

       Note:  As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". When Postfix <= 2.5  is  linked  against  OpenSSL  1.0.1  or
       later,  these,  or  any other new protocol versions, cannot be disabled
       except by also disabling "TLSv1" (typically leaving just "SSLv3").  The
       latest  patch  levels of Postfix >= 2.6, and all versions of Postfix >=
       2.10 can explicitly disable support for "TLSv1.1" or "TLSv1.2".

       OpenSSL 1.1.1 introduces support for "TLSv1.3".  With  Postfix  >=  3.4
       (or patch releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2) this can be dis-
       abled, if need be, via "!TLSv1.3".

       At the dane and dane-only security levels, when usable TLSA records are
       obtained  for  the remote SMTP server, the Postfix SMTP client is obli-
       gated to include the SNI TLS extension in its SSL client hello message.
       This  may help the remote SMTP server live up to its promise to provide
       a certificate that matches its TLSA records.  Since TLS extensions  re-
       quire  TLS  1.0  or later, the Postfix SMTP client must disable "SSLv2"
       and "SSLv3" when SNI is required.  If you use "dane" or "dane-only"  do
       not disable TLSv1, except perhaps via the policy table for destinations
       which you are sure will support "TLSv1.1" or "TLSv1.2".

       See  the  documentation  of  the  smtp_tls_policy_maps  parameter   and
       TLS_README for more information about security levels.

       Example:

       # Preferred syntax with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Legacy syntax:
       smtp_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
       Log the hostname of a remote SMTP server that offers STARTTLS, when TLS
       is not already enabled for that server.

       The logfile record looks like:

       postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

       This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS usage policy by
       next-hop  destination  and  by  remote SMTP server hostname.  When both
       lookups succeed, the more specific per-site policy  (NONE,  MUST,  etc)
       overrides  the  less  specific  one (MAY), and the more secure per-site
       policy (MUST, etc) overrides the less secure one (NONE).  With  Postfix
       2.3   and   later   smtp_tls_per_site   is  strongly  discouraged:  use
       smtp_tls_policy_maps instead.

       Use of the bare hostname as the per-site table lookup key  is  discour-
       aged.  Always  use  the full destination nexthop (enclosed in [] with a
       possible ":port" suffix). A recipient domain  or  MX-enabled  transport
       next-hop  with  no  port  suffix  may look like a bare hostname, but is
       still a suitable destination.

       Specify a next-hop destination or  server  hostname  on  the  left-hand
       side;  no wildcards are allowed. The next-hop destination is either the
       recipient domain, or the destination specified with a transport(5)  ta-
       ble, the relayhost parameter, or the relay_transport parameter.  On the
       right hand side specify one of the following keywords:

       NONE   Don't use TLS at all. This overrides a less specific MAY  lookup
              result from the alternate host or next-hop lookup key, and over-
              rides   the   global   smtp_use_tls,    smtp_enforce_tls,    and
              smtp_tls_enforce_peername settings.

       MAY    Try  to  use  TLS if the server announces support, otherwise use
              the unencrypted connection. This has less precedence than a more
              specific  result  (including  NONE)  from  the alternate host or
              next-hop lookup key, and has less precedence than the more  spe-
              cific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peer-
              name = yes".

       MUST_NOPEERMATCH
              Require TLS encryption, but do not require that the remote  SMTP
              server  hostname  matches  the  information  in  the remote SMTP
              server certificate, or that the server certificate was issued by
              a  trusted  CA. This overrides a less secure NONE or a less spe-
              cific MAY lookup result from  the  alternate  host  or  next-hop
              lookup  key,  and  overrides  the  global smtp_use_tls, smtp_en-
              force_tls and smtp_tls_enforce_peername settings.

       MUST   Require TLS encryption, require  that  the  remote  SMTP  server
              hostname  matches the information in the remote SMTP server cer-
              tificate, and require that the remote  SMTP  server  certificate
              was  issued  by  a trusted CA. This overrides a less secure NONE
              and MUST_NOPEERMATCH or a less specific MAY lookup  result  from
              the  alternate  host  or  next-hop lookup key, and overrides the
              global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peer-
              name settings.

       The above keywords correspond to the "none", "may", "encrypt" and "ver-
       ify" security levels for the new smtp_tls_security_level parameter  in-
       troduced  in  Postfix 2.3. Starting with Postfix 2.3, and independently
       of how the policy  is  specified,  the  smtp_tls_mandatory_ciphers  and
       smtp_tls_mandatory_protocols  parameters  apply  when TLS encryption is
       mandatory. Connections for which encryption is optional  typically  en-
       able  all  "export"  grade and better ciphers (see smtp_tls_ciphers and
       smtp_tls_protocols).

       As long as no secure DNS lookup mechanism is available, false hostnames
       in  MX  or  CNAME responses can change the server hostname that Postfix
       uses for TLS policy lookup and server  certificate  verification.  Even
       with  a  perfect  match between the server hostname and the server cer-
       tificate, there is no guarantee that Postfix is connected to the  right
       server.   See TLS_README (Closing a DNS loophole with obsolete per-site
       TLS policies) for a possible work-around.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS security policy
       by next-hop destination; when a  non-empty  value  is  specified,  this
       overrides the obsolete smtp_tls_per_site parameter.  See TLS_README for
       a more detailed discussion of TLS security levels.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       The TLS policy table is indexed by the full next-hop destination, which
       is  either  the recipient domain, or the verbatim next-hop specified in
       the  transport  table,   $local_transport,   $virtual_transport,   $re-
       lay_transport or $default_transport. This includes any enclosing square
       brackets and any non-default destination server port suffix.  The  LMTP
       socket type prefix (inet: or unix:) is not included in the lookup key.

       Only  the  next-hop  domain,  or $myhostname with LMTP over UNIX-domain
       sockets, is used as the nexthop name for certificate verification.  The
       port  and  any  enclosing  square brackets are used in the table lookup
       key, but are not used for server name verification.

       When the lookup key is a domain name without enclosing square  brackets
       or  any :port suffix (typically the recipient domain), and the full do-
       main is not found in the table, just as with  the  transport(5)  table,
       the  parent  domain starting with a leading "." is matched recursively.
       This allows one to specify a security policy for a recipient domain and
       all its sub-domains.

       The  lookup result is a security level, followed by an optional list of
       whitespace and/or comma separated name=value attributes  that  override
       related  main.cf settings. The TLS security levels in order of increas-
       ing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic TLS. Since sending in the clear is acceptable, de-
              manding stronger than default TLS security merely reduces inter-
              operability. The optional "ciphers", "exclude", and  "protocols"
              attributes (available for opportunistic TLS with Postfix >= 2.6)
              and "connection_reuse" attribute (Postfix >= 3.4)  override  the
              "smtp_tls_ciphers", "smtp_tls_exclude_ciphers", "smtp_tls_proto-
              cols", and "smtp_tls_connection_reuse" configuration parameters.
              When opportunistic TLS handshakes fail, Postfix retries the con-
              nection with TLS disabled.  This allows mail delivery  to  sites
              with non-interoperable TLS implementations.

       encrypt
              Mandatory TLS encryption. At this level and higher, the optional
              "protocols"  attribute  overrides  the  main.cf  smtp_tls_manda-
              tory_protocols parameter, the optional "ciphers" attribute over-
              rides the main.cf smtp_tls_mandatory_ciphers parameter, the  op-
              tional  "exclude"  attribute  (Postfix  >=  2.6)  overrides  the
              main.cf smtp_tls_mandatory_exclude_ciphers  parameter,  and  the
              optional "connection_reuse" attribute (Postfix >= 3.4) overrides
              the main.cf smtp_tls_connection_reuse parameter. In  the  policy
              table,  multiple protocols or excluded ciphers must be separated
              by colons, as attribute values may  not  contain  whitespace  or
              commas.

       dane   Opportunistic  DANE  TLS.  The TLS policy for the destination is
              obtained via TLSA records in DNSSEC.  If  no  TLSA  records  are
              found,  the  effective  security  level  used  is  may.  If TLSA
              records are found, but none are usable, the  effective  security
              level is encrypt.  When usable TLSA records are obtained for the
              remote SMTP server, the server certificate must match  the  TLSA
              records.   RFC 7672 (DANE) TLS authentication and DNSSEC support
              is available with Postfix 2.11 and later. The optional  "connec-
              tion_reuse"  attribute  (Postfix  >=  3.4) overrides the main.cf
              smtp_tls_connection_reuse parameter.

       dane-only
              Mandatory DANE TLS.  The TLS policy for the destination  is  ob-
              tained  via  TLSA  records  in  DNSSEC.   If no TLSA records are
              found, or none are usable, no connection is made to the  server.
              When  usable  TLSA  records  are  obtained  for  the remote SMTP
              server, the server certificate must match the TLSA records.  RFC
              7672  (DANE)  TLS authentication and DNSSEC support is available
              with Postfix 2.11 and later. The optional "connection_reuse" at-
              tribute  (Postfix >= 3.4) overrides the main.cf smtp_tls_connec-
              tion_reuse parameter.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted Certifi-
              cation Authorities.  The  certificate  trust  chain,  expiration
              date,  ...  are  not checked. Instead, the optional match attri-
              bute, or else the main.cf smtp_tls_fingerprint_cert_match param-
              eter,  lists the certificate fingerprints or the public key fin-
              gerprint (Postfix 2.9 and later) of the  valid  server  certifi-
              cate.  The digest algorithm used to calculate the fingerprint is
              selected by the smtp_tls_fingerprint_digest parameter.  Multiple
              fingerprints  can  be  combined with a "|" delimiter in a single
              match attribute, or multiple match attributes can  be  employed.
              The  ":"  character  is not used as a delimiter as it occurs be-
              tween each pair of fingerprint  (hexadecimal)  digits.  The  op-
              tional  "connection_reuse"  attribute (Postfix >= 3.4) overrides
              the main.cf smtp_tls_connection_reuse parameter.

       verify Mandatory TLS verification.  At  this  security  level,  DNS  MX
              lookups  are  trusted to be secure enough, and the name verified
              in the server certificate is  usually  obtained  indirectly  via
              unauthenticated  DNS MX lookups.  The optional "match" attribute
              overrides the main.cf smtp_tls_verify_cert_match  parameter.  In
              the policy table, multiple match patterns and strategies must be
              separated by colons.  In practice explicit control over matching
              is  more  common  with the "secure" policy, described below. The
              optional "connection_reuse" attribute (Postfix >= 3.4) overrides
              the main.cf smtp_tls_connection_reuse parameter.

       secure Secure-channel  TLS.  At  this  security  level, DNS MX lookups,
              though potentially used  to  determine  the  candidate  next-hop
              gateway  IP  addresses,  are not trusted to be secure enough for
              TLS peername verification. Instead, the default name verified in
              the  server  certificate is obtained directly from the next-hop,
              or is explicitly specified  via  the  optional  match  attribute
              which  overrides  the main.cf smtp_tls_secure_cert_match parame-
              ter. In the policy table, multiple match patterns and strategies
              must be separated by colons.  The match attribute is most useful
              when multiple domains are supported by common server, the policy
              entries  for  additional  domains specify matching rules for the
              primary domain  certificate.  While  transport  table  overrides
              routing  the secondary domains to the primary nexthop also allow
              secure verification, they risk delivery to the wrong destination
              when  domains  change  hands or are re-assigned to new gateways.
              With the "match" attribute approach, routing is  not  perturbed,
              and mail is deferred if verification of a new MX host fails. The
              optional "connection_reuse" attribute (Postfix >= 3.4) overrides
              the main.cf smtp_tls_connection_reuse parameter.

       Example:

       /etc/postfix/main.cf:
           smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
           # Postfix 2.5 and later
           smtp_tls_fingerprint_digest = md5

       /etc/postfix/tls_policy:
           example.edu                 none
           example.mil                 may
           example.gov                 encrypt protocols=TLSv1
           example.com                 verify ciphers=high
           example.net                 secure
           .example.net                secure match=.example.net:example.net
           [mail.example.org]:587      secure match=nexthop
           # Postfix 2.5 and later
           [thumb.example.org]          fingerprint
               match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
               match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

       Note:  The  hostname  strategy  if  listed  in a non-default setting of
       smtp_tls_secure_cert_match or in the match attribute in the policy  ta-
       ble  can  render the secure level vulnerable to DNS forgery. Do not use
       the hostname strategy for secure-channel configurations in environments
       where DNS security is not assured.

       This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2, !SSLv3)
       List  of TLS protocols that the Postfix SMTP client will exclude or in-
       clude with opportunistic TLS encryption. The default value is  "!SSLv2,
       !SSLv3"  for  Postfix  releases  after the middle of 2015, "!SSLv2" for
       older releases. Before Postfix 2.6, the Postfix SMTP client  would  use
       all protocols with opportunistic TLS.

       In main.cf the values are separated by whitespace, commas or colons. In
       the policy table (see smtp_tls_policy_maps) the only valid separator is
       colon.  An  empty  value  means allow all protocols. The valid protocol
       names, (see \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       The range of protocols advertised by an SSL/TLS client must be contigu-
       ous.   When a protocol version is enabled, disabling any higher version
       implicitly disables all versions above that higher version.  Thus,  for
       example (assuming the OpenSSL library supports both SSLv2 and SSLv3):

           smtp_tls_protocols = !SSLv2, !TLSv1
       also  disables  any  protocols  version  higher than TLSv1 leaving only
       "SSLv3" enabled.

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1"  and
       "TLSv1.2".  The latest patch levels of Postfix >= 2.6, and all versions
       of Postfix >= 2.10 can explicitly  disable  support  for  "TLSv1.1"  or
       "TLSv1.2"

       OpenSSL  1.1.1  introduces  support for "TLSv1.3".  With Postfix >= 3.4
       (or patch releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2) this can be dis-
       abled, if need be, via "!TLSv1.3".

       To  include  a  protocol  list its name, to exclude it, prefix the name
       with a "!" character.  To  exclude  SSLv2  for  opportunistic  TLS  set
       "smtp_tls_protocols  = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols
       to  include,  rather  than  protocols to exclude, is supported, but not
       recommended.  The exclusion form more closely  matches  the  underlying
       OpenSSL interface semantics.

       Example:
       # TLSv1 or better:
       smtp_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)
       The  verification depth for remote SMTP server certificates. A depth of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for  compati-
       bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
       value was 5, but the limit was not actually enforced. If you  have  set
       this  to  a  lower  non-default  value,  certificates with longer trust
       chains may now fail to verify. Certificate chains with 1 or 2  CAs  are
       common,  deeper  chains  are  more  rare and any number between 5 and 9
       should suffice in practice. You can choose a lower number if, for exam-
       ple,  you  trust  certificates directly signed by an issuing CA but not
       any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
       How the Postfix SMTP client verifies the  server  certificate  peername
       for  the  "secure"  TLS  security level. In a "secure" TLS policy table
       ($smtp_tls_policy_maps) entry the optional "match" attribute  overrides
       this main.cf setting.

       This  parameter  specifies one or more patterns or strategies separated
       by commas, whitespace or colons.  In the policy table  the  only  valid
       separator is the colon character.

       For   a  description  of  the  pattern  and  strategy  syntax  see  the
       smtp_tls_verify_cert_match parameter. The "hostname" strategy should be
       avoided  in this context, as in the absence of a secure global DNS, us-
       ing the results of MX lookups in certificate verification is not immune
       to active (man-in-the-middle) attacks on DNS.

       Sample main.cf setting:

           smtp_tls_secure_cert_match = nexthop

       Sample policy table override:

           example.net     secure match=example.com:.example.com
           .example.net    secure match=example.com:.example.com

       This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
       The default SMTP TLS security level for the Postfix SMTP client; when a
       non-empty value is specified, this overrides  the  obsolete  parameters
       smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.

       Specify one of the following security levels:

       none   No  TLS. TLS will not be used unless enabled for specific desti-
              nations via smtp_tls_policy_maps.

       may    Opportunistic TLS. Use TLS if this is supported  by  the  remote
              SMTP server, otherwise use plaintext. Since sending in the clear
              is acceptable, demanding  stronger  than  default  TLS  security
              merely  reduces  interoperability.   The  "smtp_tls_ciphers" and
              "smtp_tls_protocols" (Postfix >= 2.6)  configuration  parameters
              provide  control  over  the protocols and cipher grade used with
              opportunistic TLS.  With earlier releases the opportunistic  TLS
              cipher  grade  is always "export" and no protocols are disabled.
              When TLS handshakes fail, the connection  is  retried  with  TLS
              disabled.   This allows mail delivery to sites with non-interop-
              erable TLS implementations.

       encrypt
              Mandatory TLS encryption. Since a minimum level of  security  is
              intended, it is reasonable to be specific about sufficiently se-
              cure protocol versions and ciphers. At this security  level  and
              higher,  the main.cf parameters smtp_tls_mandatory_protocols and
              smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
              cipher grade which the administrator considers secure enough for
              mandatory encrypted sessions. This security level is not an  ap-
              propriate default for systems delivering mail to the Internet.

       dane   Opportunistic  DANE TLS.  At this security level, the TLS policy
              for the destination is obtained via DNSSEC.  For TLSA policy  to
              be  in effect, the destination domain's containing DNS zone must
              be signed and the Postfix SMTP client's operating system must be
              configured to send its DNS queries to a recursive DNS nameserver
              that is able to validate the signed records.  Each MX host's DNS
              zone  should  also  be signed, and should publish DANE TLSA (RFC
              7672) records that specify how that MX host's TLS certificate is
              to  be verified.  TLSA records do not preempt the normal SMTP MX
              host selection algorithm, if some MX hosts support TLSA and oth-
              ers  do  not,  TLS security will vary from delivery to delivery.
              It is up to the domain owner to configure  their  MX  hosts  and
              their  DNS  sensibly.   To configure the Postfix SMTP client for
              DNSSEC lookups  see  the  documentation  for  the  smtp_dns_sup-
              port_level   main.cf   parameter.   When  DNSSEC-validated  TLSA
              records are not found the effective tls security level is "may".
              When  TLSA records are found, but are all unusable the effective
              security level is "encrypt".  For purposes of protocol  and  ci-
              pher  selection,  the  "dane"  security  level is treated like a
              "mandatory" TLS security level, and weak ciphers  and  protocols
              are  disabled.  Since DANE authenticates server certificates the
              "aNULL" cipher-suites are transparently excluded at this  level,
              no need to configure this manually.  RFC 7672 (DANE) TLS authen-
              tication is available with Postfix 2.11 and later.

       dane-only
              Mandatory DANE TLS.  This is just like "dane"  above,  but  DANE
              TLSA  authentication is required.  There is no fallback to "may"
              or "encrypt" when TLSA records are  missing  or  unusable.   RFC
              7672  (DANE)  TLS  authentication is available with Postfix 2.11
              and later.

       fingerprint
              Certificate fingerprint verification.  At this  security  level,
              there are no trusted Certification Authorities.  The certificate
              trust chain, expiration date, etc., are  not  checked.  Instead,
              the smtp_tls_fingerprint_cert_match parameter lists the certifi-
              cate fingerprint or public  key  fingerprint  (Postfix  2.9  and
              later)  of  the  valid  server certificate. The digest algorithm
              used  to  calculate  the  fingerprint   is   selected   by   the
              smtp_tls_fingerprint_digest  parameter.  Available  with Postfix
              2.5 and later.

       verify Mandatory TLS verification.  At  this  security  level,  DNS  MX
              lookups  are  trusted to be secure enough, and the name verified
              in the server certificate is  usually  obtained  indirectly  via
              unauthenticated  DNS  MX lookups. The smtp_tls_verify_cert_match
              parameter controls how the server name is verified. In  practice
              explicit  control  over  matching is more common at the "secure"
              level, described below. This security level is not an  appropri-
              ate default for systems delivering mail to the Internet.

       secure Secure-channel  TLS.   At  this  security level, DNS MX lookups,
              though potentially used  to  determine  the  candidate  next-hop
              gateway  IP  addresses,  are not trusted to be secure enough for
              TLS peername verification. Instead, the default name verified in
              the  server  certificate is obtained from the next-hop domain as
              specified in the smtp_tls_secure_cert_match configuration param-
              eter.  The  default  matching  rule is that a server certificate
              matches when its name is equal to or is a sub-domain of the nex-
              thop  domain.  This security level is not an appropriate default
              for systems delivering mail to the Internet.

       Examples:

       # No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
       smtp_tls_security_level = none

       # Opportunistic TLS.
       smtp_tls_security_level = may
       # Postfix >= 2.6:
       # Do not tweak opportunistic ciphers or protocol unless it is essential
       # to do so (if a security vulnerability is found in the SSL library that
       # can be mitigated by disabling a particular protocol or raising the
       # cipher grade from "export" to "low" or "medium").
       smtp_tls_ciphers = export
       smtp_tls_protocols = !SSLv2, !SSLv3

       # Mandatory (high-grade) TLS encryption.
       smtp_tls_security_level = encrypt
       smtp_tls_mandatory_ciphers = high

       # Mandatory TLS verification of hostname or nexthop domain.
       smtp_tls_security_level = verify
       smtp_tls_mandatory_ciphers = high
       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       # Secure channel TLS with exact nexthop name match.
       smtp_tls_security_level = secure
       smtp_tls_mandatory_protocols = TLSv1
       smtp_tls_mandatory_ciphers = high
       smtp_tls_secure_cert_match = nexthop

       # Certificate fingerprint verification (Postfix >= 2.5).
       # The CA-less "fingerprint" security level only scales to a limited
       # number of destinations. As a global default rather than a per-site
       # setting, this is practical when mail for all recipients is sent
       # to a central mail hub.
       relayhost = [mailhub.example.com]
       smtp_tls_security_level = fingerprint
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       smtp_tls_mandatory_ciphers = high
       smtp_tls_fingerprint_cert_match =
           3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
           EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.3 and later.

smtp_tls_servername (default: empty)
       Optional name to send to the remote SMTP server in the TLS Server  Name
       Indication  (SNI)  extension.  The SNI extension is always on when DANE
       is used to authenticate the server, and in that case the SNI name  sent
       is the one required by RFC7672 and this parameter is ignored.

       Some  SMTP  servers  use the received SNI name to select an appropriate
       certificate chain to present to the client.  While this may improve in-
       teroperability  with  such servers, it may reduce interoperability with
       other servers that choose to abort the connection when they don't  have
       a  certificate  chain  configured for the requested name.  Such servers
       should select a default certificate chain and continue  the  handshake,
       but  some  may not.  Therefore, absent DANE, no SNI name is sent by de-
       fault.

       The SNI name must be either a valid DNS hostname, or else  one  of  the
       special  values  hostname  or  nexthop,  which select either the remote
       hostname or the nexthop domain respectively.  DNS names for SNI must be
       in  A-label (punycode) form.  Invalid DNS names log a configuration er-
       ror warning and mail delivery is deferred.

       Except when using a relayhost to forward all email, the  only  sensible
       non-empty  main.cf  setting  for  this  parameter  is  hostname.  Other
       non-empty values are only practical on a per-destination basis via  the
       servername  attribute  of the Postfix TLS policy table.  When in doubt,
       leave this  parameter  empty,  and  configure  per-destination  SNI  as
       needed.

       This feature is available in Postfix 3.4 and later.

smtp_tls_session_cache_database (default: empty)
       Name  of  the file containing the optional Postfix SMTP client TLS ses-
       sion cache. Specify a database type that supports enumeration, such  as
       btree or sdbm; there is no need to support concurrent access.  The file
       is created if it does not exist. The smtp(8) daemon does not  use  this
       parameter  directly,  rather the cache is implemented indirectly in the
       tlsmgr(8) daemon. This means that per-smtp-instance master.cf overrides
       of  this  parameter  are  not  effective.  Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
       base,  $smtp_tls_session_cache_database (and with Postfix 2.3 and later
       $lmtp_tls_session_cache_database), needs to be stored separately. It is
       not  at  this  time possible to store multiple caches in a single data-
       base.

       Note: dbm databases are not  suitable.  TLS  session  objects  are  too
       large.

       As  of version 2.5, Postfix no longer uses root privileges when opening
       this file. The file  should  now  be  stored  under  the  Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix directory is redirected to  the  Postfix-owned  data_direc-
       tory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_scache

       This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
       The  expiration  time of Postfix SMTP client TLS session cache informa-
       tion.  A cache cleanup is performed periodically  every  $smtp_tls_ses-
       sion_cache_timeout  seconds.  As with $smtp_tls_session_cache_database,
       this parameter is implemented in the  tlsmgr(8)  daemon  and  therefore
       per-smtp-instance master.cf overrides are not possible.

       As  of  Postfix 2.11 this setting cannot exceed 100 days.  If set <= 0,
       session caching is disabled.  If set to a positive value  less  than  2
       minutes, the minimum value of 2 minutes is used instead.

       This feature is available in Postfix 2.2 and later.

smtp_tls_trust_anchor_file (default: empty)
       Zero  or  more  PEM-format  files with trust-anchor certificates and/or
       public keys.  If the parameter is not empty the root CAs in CAfile  and
       CApath  are  no  longer  trusted.  Rather, the Postfix SMTP client will
       only trust certificate-chains signed by one of the  trust-anchors  con-
       tained  in  the  chosen files.  The specified trust-anchor certificates
       and public keys  are  not  subject  to  expiration,  and  need  not  be
       (self-signed) root CAs.  They may, if desired, be intermediate certifi-
       cates. Therefore, these certificates also may be found "in the  middle"
       of  the  trust  chain  presented by the remote SMTP server, and any un-
       trusted issuing parent certificates will be ignored.  Specify a list of
       pathnames separated by comma or whitespace.

       Whether  specified  in  main.cf,  or  on  a  per-destination basis, the
       trust-anchor PEM file must be accessible to the Postfix SMTP client  in
       the  chroot  jail  if applicable.  The trust-anchor file should contain
       only certificates and public keys, no private key material, and must be
       readable  by the non-privileged $mail_owner user.  This allows destina-
       tions to be bound to a set of  specific  CAs  or  public  keys  without
       trusting the same CAs for all destinations.

       The  main.cf  parameter  supports  single-purpose Postfix installations
       that send mail to a fixed  set  of  SMTP  peers.   At  most  sites,  if
       trust-anchor  files  are  used  at  all,  they  will  be specified on a
       per-destination basis via the "tafile" attribute of  the  "verify"  and
       "secure" levels in smtp_tls_policy_maps.

       The  underlying  mechanism is in support of RFC 7672 (DANE TLSA), which
       defines mechanisms for an SMTP client MTA to securely determine  server
       TLS certificates via DNS.

       If  you want your trust anchors to be public keys, with OpenSSL you can
       extract a single PEM public key from a PEM X.509 file containing a sin-
       gle certificate, as follows:

           $ openssl x509 -in cert.pem -out ta-key.pem -noout -pubkey

       This feature is available in Postfix 2.11 and later.

smtp_tls_verify_cert_match (default: hostname)
       How  the  Postfix  SMTP client verifies the server certificate peername
       for the "verify" TLS security level. In a  "verify"  TLS  policy  table
       ($smtp_tls_policy_maps)  entry the optional "match" attribute overrides
       this main.cf setting.

       This parameter specifies one or more patterns or  strategies  separated
       by  commas,  whitespace  or colons.  In the policy table the only valid
       separator is the colon character.

       Patterns specify domain names, or domain name suffixes:

       example.com
              Match the example.com domain, i.e. one of the names  the  server
              certificate  must  be example.com, upper and lower case distinc-
              tions are ignored.

       .example.com
              Match subdomains of the example.com domain, i.e. match a name in
              the server certificate that consists of a non-zero number of la-
              bels followed by a .example.com suffix.  Case  distinctions  are
              ignored.

       Strategies specify a transformation from the next-hop domain to the ex-
       pected name in the server certificate:

       nexthop
              Match against the next-hop domain, which is either the recipient
              domain,  or  the  transport  next-hop  configured for the domain
              stripped of any optional socket type  prefix,  enclosing  square
              brackets  and trailing port. When MX lookups are not suppressed,
              this is the original nexthop domain prior to the MX lookup,  not
              the  result  of the MX lookup. For LMTP delivery via UNIX-domain
              sockets, the verified next-hop name is $myhostname.  This strat-
              egy  is  suitable  for use with the "secure" policy. Case is ig-
              nored.

       dot-nexthop
              As above, but match server certificate names that are subdomains
              of the next-hop domain. Case is ignored.

       hostname
              Match  against the hostname of the server, often obtained via an
              unauthenticated DNS MX lookup. For LMTP delivery via UNIX-domain
              sockets, the verified name is $myhostname. This matches the ver-
              ification  strategy  of  the  "MUST"  keyword  in  the  obsolete
              smtp_tls_per_site  table, and is suitable for use with the "ver-
              ify" security level. When  the  next-hop  name  is  enclosed  in
              square  brackets to suppress MX lookups, the "hostname" strategy
              is the same as the "nexthop" strategy. Case is ignored.

       Sample main.cf setting:

       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       Sample policy table override:

       example.com     verify  match=hostname:nexthop
       .example.com    verify  match=example.com:.example.com:hostname

       This feature is available in Postfix 2.3 and later.

smtp_tls_wrappermode (default: no)
       Request that the Postfix SMTP client connects using  the  legacy  SMTPS
       protocol instead of using the STARTTLS command.

       This mode requires "smtp_tls_security_level = encrypt" or stronger.

       Example:  deliver  all  remote mail via a provider's server "mail.exam-
       ple.com".

       /etc/postfix/main.cf:
           # Client-side SMTPS requires "encrypt" or stronger.
           smtp_tls_security_level = encrypt
           smtp_tls_wrappermode = yes
           # The [] suppress MX lookups.
           relayhost = [mail.example.com]:465

       More examples are in TLS_README, including examples for  older  Postfix
       versions.

       This feature is available in Postfix 3.0 and later.

smtp_use_tls (default: no)
       Opportunistic  mode: use TLS when a remote SMTP server announces START-
       TLS support, otherwise send the mail in the clear.  Beware:  some  SMTP
       servers  offer  STARTTLS  even if it is not configured.  With Postfix <
       2.3, if the TLS handshake fails, and no other server is available,  de-
       livery  is  deferred  and mail stays in the queue. If this is a concern
       for you, use the smtp_tls_per_site feature instead.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)
       The  Postfix  SMTP  client time limit for sending the XFORWARD command,
       and for receiving the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
       What  remote  SMTP  clients  are  allowed to specify the XVERP command.
       This command requests that mail be delivered one recipient  at  a  time
       with a per recipient return address.

       By default, no clients are allowed to specify XVERP.

       This  parameter was renamed with Postfix version 2.1. The default value
       is backwards compatible with Postfix version 2.0.

       Specify a list of network/netmask patterns, separated by commas  and/or
       whitespace.  The  mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial   dot   causes   the  domain  to  match  any  name  below  it),
       "/file/name" or "type:table" patterns.  A "/file/name" pattern  is  re-
       placed  by  its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the  lookup  result  is  ignored).
       Continue  long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from  the  list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_authorized_verp_clients value, and in  files  specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xclient_hosts (default: empty)
       What remote SMTP clients are allowed to use the XCLIENT feature.   This
       command  overrides  remote SMTP client information that is used for ac-
       cess control. Typical use is for  SMTP-based  content  filters,  fetch-
       mail-like  programs,  or  SMTP  server  access  rule  testing.  See the
       XCLIENT_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XCLIENT.

       Specify a list of network/netmask patterns, separated by commas  and/or
       whitespace.  The  mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial   dot   causes   the  domain  to  match  any  name  below  it),
       "/file/name" or "type:table" patterns.  A "/file/name" pattern  is  re-
       placed  by  its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the  lookup  result  is  ignored).
       Continue  long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from  the  list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_authorized_xclient_hosts value, and in files  specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)
       What remote SMTP clients are allowed to use the XFORWARD feature.  This
       command  forwards  information  that  is  used to improve logging after
       SMTP-based content filters. See the XFORWARD_README  document  for  de-
       tails.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XFORWARD.

       Specify  a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the  network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial  dot  causes  the  domain  to  match  any   name   below   it),
       "/file/name"  or  "type:table" patterns.  A "/file/name" pattern is re-
       placed by its contents; a "type:table" lookup table is matched  when  a
       table  entry  matches  a  lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude  an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside  []  in
       the  smtpd_authorized_xforward_hosts value, and in files specified with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
       The  text that follows the 220 status code in the SMTP greeting banner.
       Some people like to see the mail version advertised. By default,  Post-
       fix shows no version.

       You MUST specify $myhostname at the start of the text. This is required
       by the SMTP protocol.

       Example:

       smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_auth_rate_limit (default: 0)
       The maximal number of AUTH commands that any client is allowed to  send
       to this service per time unit, regardless of whether or not Postfix ac-
       tually accepts those commands.  The time unit  is  specified  with  the
       anvil_rate_time_unit configuration parameter.

       By default, there is no limit on the number AUTH commands that a client
       may send.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 3.1 and later.

smtpd_client_connection_count_limit (default: 50)
       How many simultaneous connections any client is allowed to make to this
       service.  By default, the limit is set  to  half  the  default  process
       limit value.

       To disable this feature, specify a limit of 0.

       WARNING:  The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
       The maximal number of connection attempts any client is allowed to make
       to  this  service  per  time unit.  The time unit is specified with the
       anvil_rate_time_unit configuration parameter.

       By default, a client can make as many  connections  per  time  unit  as
       Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING:  The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
       Clients that are excluded from smtpd_client_*_count/rate_limit restric-
       tions. See the mynetworks parameter description for the parameter value
       syntax.

       By default, clients in trusted networks are excluded. Specify a list of
       network  blocks, hostnames or .domain names (the initial dot causes the
       domain to match any name below it).

       Note: IP version 6 address information must be specified inside  []  in
       the  smtpd_client_event_limit_exceptions  value, and in files specified
       with "/file/name".  IP version 6 addresses contain the  ":"  character,
       and would otherwise be confused with a "type:table" pattern.

       Pattern  matching  of domain names is controlled by the presence or ab-
       sence  of  "smtpd_client_event_limit_exceptions"  in   the   parent_do-
       main_matches_subdomains parameter value (postfix 3.0 and later).

       This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
       The  maximal number of message delivery requests that any client is al-
       lowed to make to this service per time unit, regardless of  whether  or
       not  Postfix  actually accepts those messages.  The time unit is speci-
       fied with the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many  message  delivery  requests  per
       time unit as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING:  The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
       The maximal number of new (i.e., uncached) TLS sessions that  a  remote
       SMTP  client  is  allowed to negotiate with this service per time unit.
       The time unit is specified with the anvil_rate_time_unit  configuration
       parameter.

       By default, a remote SMTP client can negotiate as many new TLS sessions
       per time unit as Postfix can accept.

       To disable this feature, specify a limit of  0.  Otherwise,  specify  a
       limit that is at least the per-client concurrent session limit, or else
       legitimate client sessions may be rejected.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.3 and later.

       Example:

       smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)
       Enable  logging of the remote SMTP client port in addition to the host-
       name and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)
       The maximal number of recipient addresses that any client is allowed to
       send  to this service per time unit, regardless of whether or not Post-
       fix actually accepts those recipients.  The time unit is specified with
       the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many recipient addresses per time unit
       as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
       Optional  restrictions that the Postfix SMTP server applies in the con-
       text of a client connection request.  See SMTPD_ACCESS_README,  section
       "Delayed  evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to allow all connection requests.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue  long  lines  by  starting the next line with whitespace.  Re-
       strictions are applied in the order as specified; the first restriction
       that matches wins.

       The  following  restrictions  are specific to client hostname or client
       network address information.

       check_ccert_access type:table
              Use the remote SMTP client certificate fingerprint or the public
              key  fingerprint  (Postfix  2.9 and later) as lookup key for the
              specified access(5) database; with Postfix version 2.2, also re-
              quire  that  the remote SMTP client certificate is verified suc-
              cessfully.  The fingerprint digest algorithm is configurable via
              the  smtpd_tls_fingerprint_digest  parameter  (hard-coded as md5
              prior to Postfix version 2.5).  This feature is  available  with
              Postfix version 2.2 and later.

       check_client_access type:table
              Search  the  specified  access database for the client hostname,
              parent domains, client  IP  address,  or  networks  obtained  by
              stripping  least  significant  octets.  See the access(5) manual
              page for details.

       check_client_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the  client  hostname,  and  execute  the  corresponding action.
              Note: a result of "OK" is not allowed for  safety  reasons.  In-
              stead,  use DUNNO in order to exclude specific hosts from black-
              lists.  This feature is available in Postfix 3.0 and later.

       check_client_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              client  hostname, and execute the corresponding action.  Note: a
              result of "OK" is not allowed for safety reasons.  Instead,  use
              DUNNO  in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.7 and later.

       check_client_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the  client  hostname,  and  execute  the  corresponding action.
              Note: a result of "OK" is not allowed for  safety  reasons.  In-
              stead,  use DUNNO in order to exclude specific hosts from black-
              lists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_access type:table
              Search the specified access database for the unverified  reverse
              client  hostname, parent domains, client IP address, or networks
              obtained by stripping least  significant  octets.  See  the  ac-
              cess(5)  manual page for details.  Note: a result of "OK" is not
              allowed for safety reasons.  Instead, use DUNNO in order to  ex-
              clude specific hosts from blacklists.  This feature is available
              in Postfix 2.6 and later.

       check_reverse_client_hostname_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the  unverified  reverse client hostname, and execute the corre-
              sponding action.  Note: a result of  "OK"  is  not  allowed  for
              safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 3.0
              and later.

       check_reverse_client_hostname_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              unverified reverse client hostname, and execute the  correspond-
              ing  action.   Note:  a result of "OK" is not allowed for safety
              reasons.  Instead, use DUNNO in order to exclude specific  hosts
              from  blacklists.   This feature is available in Postfix 2.7 and
              later.

       check_reverse_client_hostname_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the  unverified  reverse client hostname, and execute the corre-
              sponding action.  Note: a result of  "OK"  is  not  allowed  for
              safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 2.7
              and later.

       check_sasl_access type:table
              Use  the remote SMTP client SASL user name as lookup key for the
              specified access(5) database. The lookup key has the form "user-
              name@domainname"   when  the  smtpd_sasl_local_domain  parameter
              value is non-empty.   Unlike  the  check_client_access  feature,
              check_sasl_access  does not perform matches of parent domains or
              IP subnet ranges.  This feature is available with  Postfix  ver-
              sion 2.11 and later.

       permit_inet_interfaces
              Permit  the request when the client IP address matches $inet_in-
              terfaces.

       permit_mynetworks
              Permit the request when the client IP address matches  any  net-
              work or network address listed in  $mynetworks.

       permit_sasl_authenticated
              Permit the request when the client is successfully authenticated
              via the RFC 4954 (AUTH) protocol.

       permit_tls_all_clientcerts
              Permit the request when the remote SMTP  client  certificate  is
              verified  successfully.  This option must be used only if a spe-
              cial CA issues the certificates and only this CA  is  listed  as
              trusted  CA.  Otherwise,  clients with a third-party certificate
              would also be allowed to relay.  Specify  "tls_append_default_CA
              =  no" when the trusted CA is specified with smtpd_tls_CAfile or
              smtpd_tls_CApath, to prevent Postfix  from  appending  the  sys-
              tem-supplied  default CAs.  This feature is available with Post-
              fix version 2.2.

       permit_tls_clientcerts
              Permit the request when the remote SMTP client certificate  fin-
              gerprint  or  public  key fingerprint (Postfix 2.9 and later) is
              listed in $relay_clientcerts.  The fingerprint digest  algorithm
              is  configurable  via the smtpd_tls_fingerprint_digest parameter
              (hard-coded as md5 prior to Postfix version 2.5).  This  feature
              is available with Postfix version 2.2.

       reject_rbl_client rbl_domain=d.d.d.d
              Reject  the  request when the reversed client network address is
              listed with the A record  "d.d.d.d"  under  rbl_domain  (Postfix
              version 2.1 and later only).  Each "d" is a number, or a pattern
              inside "[]" that contains one or more ";"-separated  numbers  or
              number..number  ranges  (Postfix  version 2.8 and later).  If no
              "=d.d.d.d" is specified, reject the request  when  the  reversed
              client network address is listed with any A record under rbl_do-
              main.
              The maps_rbl_reject_code parameter specifies the  response  code
              for  rejected  requests  (default:   554), the default_rbl_reply
              parameter specifies the default server reply,  and  the  rbl_re-
              ply_maps  parameter specifies tables with server replies indexed
              by rbl_domain.  This feature is available  in  Postfix  2.0  and
              later.

       permit_dnswl_client dnswl_domain=d.d.d.d
              Accept  the  request when the reversed client network address is
              listed with the A record "d.d.d.d" under dnswl_domain.  Each "d"
              is  a number, or a pattern inside "[]" that contains one or more
              ";"-separated  numbers  or   number..number   ranges.    If   no
              "=d.d.d.d"  is  specified,  accept the request when the reversed
              client network  address  is  listed  with  any  A  record  under
              dnswl_domain.
              For  safety,  permit_dnswl_client  is  silently  ignored when it
              would override reject_unauth_destination.   The  result  is  DE-
              FER_IF_REJECT  when  whitelist  lookup  fails.   This feature is
              available in Postfix 2.8 and later.

       reject_rhsbl_client rbl_domain=d.d.d.d
              Reject the request when the client hostname is listed with the A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
              only).  Each "d" is a number, or a pattern inside "[]" that con-
              tains one or more ";"-separated numbers or number..number ranges
              (Postfix version 2.8 and later).  If no "=d.d.d.d" is specified,
              reject the request when the client hostname is listed with any A
              record under rbl_domain. See the  reject_rbl_client  description
              above for additional RBL related configuration parameters.  This
              feature is available in Postfix 2.0 and later; with Postfix ver-
              sion  2.8  and  later,  reject_rhsbl_reverse_client will usually
              produce better results.

       permit_rhswl_client rhswl_domain=d.d.d.d
              Accept the request when the client hostname is listed with the A
              record "d.d.d.d" under rhswl_domain.  Each "d" is a number, or a
              pattern inside "[]" that contains one or more ";"-separated num-
              bers  or  number..number  ranges. If no "=d.d.d.d" is specified,
              accept the request when the client hostname is listed with any A
              record under rhswl_domain.
              Caution:  client  name whitelisting is fragile, since the client
              name lookup can fail due  to  temporary  outages.   Client  name
              whitelisting  should  be  used only to reduce false positives in
              e.g.  DNS-based blocklists, and not for making access  rule  ex-
              ceptions.
              For  safety,  permit_rhswl_client  is  silently  ignored when it
              would override reject_unauth_destination.   The  result  is  DE-
              FER_IF_REJECT  when  whitelist  lookup  fails.   This feature is
              available in Postfix 2.8 and later.

       reject_rhsbl_reverse_client rbl_domain=d.d.d.d
              Reject the request when the unverified reverse  client  hostname
              is  listed  with  the A record "d.d.d.d" under rbl_domain.  Each
              "d" is a number, or a pattern inside "[]" that contains  one  or
              more  ";"-separated  numbers  or  number..number  ranges.  If no
              "=d.d.d.d" is specified, reject the request when the  unverified
              reverse  client  hostname  is  listed  with  any  A record under
              rbl_domain. See the reject_rbl_client description above for  ad-
              ditional  RBL related configuration parameters.  This feature is
              available in Postfix 2.8 and later.

       reject_unknown_client_hostname  (with   Postfix   <   2.3:   reject_un-
       known_client)
              Reject  the  request when 1) the client IP address->name mapping
              fails,  or  2)  the  name->address  mapping  fails,  or  3)  the
              name->address mapping does not match the client IP address.
              This  is  a  stronger  restriction  than  the reject_unknown_re-
              verse_client_hostname feature, which triggers only under  condi-
              tion 1) above.
              The  unknown_client_reject_code parameter specifies the response
              code for rejected requests (default: 450). The reply  is  always
              450 in case the address->name or name->address lookup failed due
              to a temporary problem.

       reject_unknown_reverse_client_hostname
              Reject the request  when  the  client  IP  address  has  no  ad-
              dress->name mapping.
              This    is    a   weaker   restriction   than   the   reject_un-
              known_client_hostname feature, which requires not only that  the
              address->name  and  name->address  mappings exist, but also that
              the two mappings reproduce the client IP address.
              The unknown_client_reject_code parameter specifies the  response
              code  for rejected requests (default: 450).  The reply is always
              450 in case the address->name lookup failed due to  a  temporary
              problem.
              This feature is available in Postfix 2.3 and later.

       In  addition,  you  can  use any of the following generic restrictions.
       These restrictions are applicable in any SMTP command context.

       check_policy_service servername
              Query the specified policy server. See  the  SMTPD_POLICY_README
              document  for  details. This feature is available in Postfix 2.1
              and later.

       defer  Defer the request. The client is told to try again  later.  This
              restriction  is useful at the end of a restriction list, to make
              the default policy explicit.
              The defer_code parameter specifies the SMTP  server  reply  code
              (default: 450).

       defer_if_permit
              Defer  the  request if some later restriction would result in an
              explicit or implicit PERMIT  action.   This  is  useful  when  a
              blacklisting  feature  fails  due  to a temporary problem.  This
              feature is available in Postfix version 2.1 and later.

       defer_if_reject
              Defer the request if some later restriction would  result  in  a
              REJECT action.  This is useful when a whitelisting feature fails
              due to a temporary problem.  This feature is available in  Post-
              fix version 2.1 and later.

       permit Permit  the  request. This restriction is useful at the end of a
              restriction list, to make the default policy explicit.

       reject_multi_recipient_bounce
              Reject the request when the envelope sender is the null address,
              and the message has multiple envelope recipients. This usage has
              rare but  legitimate  applications:  under  certain  conditions,
              multi-recipient  mail  that  was  posted with the DSN option NO-
              TIFY=NEVER may be forwarded with the null sender address.
              Note: this restriction can  only  work  reliably  when  used  in
              smtpd_data_restrictions  or  smtpd_end_of_data_restrictions, be-
              cause the total number of recipients is not known at an  earlier
              stage of the SMTP conversation.  Use at the RCPT stage will only
              reject the second etc.  recipient.
              The multi_recipient_bounce_reject_code parameter  specifies  the
              response  code for rejected requests (default:  550).  This fea-
              ture is available in Postfix 2.1 and later.

       reject_plaintext_session
              Reject the request when the connection is  not  encrypted.  This
              restriction  should  not  be  used  before  the client has had a
              chance to negotiate encryption with the AUTH  or  STARTTLS  com-
              mands.
              The  plaintext_reject_code parameter specifies the response code
              for rejected requests (default:  450).  This feature  is  avail-
              able in Postfix 2.3 and later.

       reject_unauth_pipelining
              Reject  the request when the client sends SMTP commands ahead of
              time where it is not allowed, or when the client sends SMTP com-
              mands  ahead  of time without knowing that Postfix actually sup-
              ports ESMTP command pipelining. This stops mail from  bulk  mail
              software  that improperly uses ESMTP command pipelining in order
              to speed up deliveries.
              With Postfix 2.6 and later, the SMTP server sets  a  per-session
              flag whenever it detects illegal pipelining, including pipelined
              HELO or EHLO commands. The reject_unauth_pipelining feature sim-
              ply  tests  whether the flag was set at any point in time during
              the session.
              With older Postfix versions, reject_unauth_pipelining checks the
              current  status  of  the  input read queue, and its usage is not
              recommended in contexts other than smtpd_data_restrictions.

       reject Reject the request. This restriction is useful at the end  of  a
              restriction  list, to make the default policy explicit.  The re-
              ject_code configuration parameter specifies  the  response  code
              for rejected requests (default: 554).

       sleep seconds
              Pause  for  the specified number of seconds and proceed with the
              next restriction in the list, if any. This may stop zombie  mail
              when used as:
              /etc/postfix/main.cf:
                  smtpd_client_restrictions =
                      sleep 1, reject_unauth_pipelining
                  smtpd_delay_reject = no
              This feature is available in Postfix 2.3.

       warn_if_reject
              A safety net for testing. When "warn_if_reject" is placed before
              a reject-type restriction, access  table  query,  or  check_pol-
              icy_service  query, this logs a "reject_warning" message instead
              of rejecting a request (when a reject-type restriction fails due
              to  a  temporary error, this logs a "reject_warning" message for
              any implicit "defer_if_permit" actions that would normally  pre-
              vent mail from being accepted by some later access restriction).
              This feature has no effect on defer_if_reject restrictions.

       Other restrictions that are valid in this context:

       o      SMTP command specific restrictions that are described under  the
              smtpd_helo_restrictions,  smtpd_sender_restrictions or smtpd_re-
              cipient_restrictions parameters. When helo, sender or  recipient
              restrictions  are  listed  under smtpd_client_restrictions, they
              have effect  only  with  "smtpd_delay_reject  =  yes",  so  that
              $smtpd_client_restrictions  is evaluated at the time of the RCPT
              TO command.

       Example:

       smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)
       A mechanism to transform commands from remote SMTP clients.  This is  a
       last-resort  tool  to work around client commands that break interoper-
       ability with the Postfix SMTP server.  Other uses involve fault  injec-
       tion to test Postfix's handling of invalid commands.

       Specify  the  name of a "type:table" lookup table. The search string is
       the SMTP command as received from the remote SMTP client,  except  that
       initial  whitespace  and the trailing <CR><LF> are removed.  The result
       value is executed by the Postfix SMTP server.

       There is no need to use smtpd_command_filter for the following cases:

       o      Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

       o      Postfix already accepts the correct form "user@[ipaddress]". Use
              virtual_alias_maps or canonical_maps to translate these into do-
              main names if necessary.

       o      Use "strict_rfc821_envelopes = no" to accept "RCPT TO:<User Name
              _user@example.com__".  Postfix  will ignore the "User Name" part
              and deliver to the _user@example.com_ address.

       Examples of problems that can be solved with  the  smtpd_command_filter
       feature:

       /etc/postfix/main.cf:
           smtpd_command_filter = pcre:/etc/postfix/command_filter

       /etc/postfix/command_filter:
           # Work around clients that send malformed HELO commands.
           /^HELO\s*$/ HELO domain.invalid

           # Work around clients that send empty lines.
           /^\s*$/     NOOP

           # Work around clients that send RCPT TO:<'user@domain'>.
           # WARNING: do not lose the parameters that follow the address.
           /^(RCPT\s+TO:\s*<)'([^[:space:]]+)'(>.*)/     $1$2$3

           # Append XVERP to MAIL FROM commands to request VERP-style delivery.
           # See VERP_README for more information on how to use Postfix VERP.
           /^(MAIL FROM:\s*<listname@example\.com>.*)/   $1 XVERP

           # Bounce-never mail sink. Use notify_classes=bounce,resource,software
           # to send bounced mail to the postmaster (with message body removed).
           /^(RCPT\s+TO:\s*<.*>.*)\s+NOTIFY=\S+(.*)/     $1 NOTIFY=NEVER$2
           /^(RCPT\s+TO:.*)/                             $1 NOTIFY=NEVER

       This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)
       Optional  access  restrictions  that the Postfix SMTP server applies in
       the context of the SMTP DATA command.  See SMTPD_ACCESS_README, section
       "Delayed  evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       This feature is available in Postfix 2.0 and later.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue  long  lines  by  starting the next line with whitespace.  Re-
       strictions are applied in the order as specified; the first restriction
       that matches wins.

       The following restrictions are valid in this context:

       o      Generic  restrictions  that can be used in any SMTP command con-
              text, described under smtpd_client_restrictions.

       o      SMTP   command    specific    restrictions    described    under
              smtpd_client_restrictions,              smtpd_helo_restrictions,
              smtpd_sender_restrictions or smtpd_recipient_restrictions.

       o      However, no recipient information is available in  the  case  of
              multi-recipient mail. Acting on only one recipient would be mis-
              leading,  because  any  decision  will  affect  all   recipients
              equally.  Acting on all recipients would require a possibly very
              large amount of memory, and would also  be  misleading  for  the
              reasons mentioned before.

       Examples:

       smtpd_data_restrictions = reject_unauth_pipelining
       smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
       Postpone  the  start  of an SMTP mail transaction until a valid RCPT TO
       command is received. Specify "no" to create a mail transaction as  soon
       as the Postfix SMTP server receives a valid MAIL FROM command.

       With  sites  that  reject lots of mail, the default setting reduces the
       use of disk, CPU and memory resources. The downside  is  that  rejected
       recipients  are  logged  with NOQUEUE instead of a mail transaction ID.
       This complicates the logfile analysis of multi-recipient mail.

       This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
       Wait until the RCPT TO command before evaluating $smtpd_client_restric-
       tions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait
       until the ETRN command before evaluating $smtpd_client_restrictions and
       $smtpd_helo_restrictions.

       This  feature  is  turned on by default because some clients apparently
       mis-behave when the Postfix SMTP server rejects  commands  before  RCPT
       TO.

       The default setting has one major benefit: it allows Postfix to log re-
       cipient address information when rejecting  a  client  name/address  or
       sender  address, so that it is possible to find out whose mail is being
       rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP client address, with case in-
       sensitive  lists  of  EHLO  keywords (pipelining, starttls, auth, etc.)
       that the Postfix SMTP server will not send in the EHLO  response  to  a
       remote  SMTP  client. See smtpd_discard_ehlo_keywords for details.  The
       tables are not searched by hostname for robustness reasons.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining,  starttls,  auth,
       etc.)  that  the Postfix SMTP server will not send in the EHLO response
       to a remote SMTP client.

       This feature is available in Postfix 2.2 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

       o      Use  the smtpd_discard_ehlo_keyword_address_maps feature to dis-
              card EHLO keywords selectively.

smtpd_dns_reply_filter (default: empty)
       Optional filter for  Postfix  SMTP  server  DNS  lookup  results.   See
       smtp_dns_reply_filter for details including an example.

       This feature is available in Postfix 3.0 and later.

smtpd_end_of_data_restrictions (default: empty)
       Optional  access  restrictions  that the Postfix SMTP server applies in
       the context of the SMTP END-OF-DATA command.  See  SMTPD_ACCESS_README,
       section  "Delayed  evaluation  of  SMTP access restriction lists" for a
       discussion of evaluation context and time.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for details and limitations.

smtpd_enforce_tls (default: no)
       Mandatory TLS: announce STARTTLS support to remote  SMTP  clients,  and
       require  that  clients  use TLS encryption.  According to RFC 2487 this
       MUST NOT be applied in case of a publicly-referenced SMTP server.  This
       option is therefore off by default.

       Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

       Note  2:  when  invoked  via  "sendmail  -bs", Postfix will never offer
       STARTTLS due to insufficient privileges to access  the  server  private
       key. This is intended behavior.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)
       With Postfix version 2.1 and later: the SMTP server response delay  af-
       ter  a  client  has  made more than $smtpd_soft_error_limit errors, and
       fewer than $smtpd_hard_error_limit errors, without delivering mail.

       With Postfix version 2.0 and earlier:  the  SMTP  server  delay  before
       sending  a reject (4xx or 5xx) response, when the client has made fewer
       than $smtpd_soft_error_limit errors without delivering mail.

smtpd_etrn_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the  con-
       text  of  a client ETRN command.  See SMTPD_ACCESS_README, section "De-
       layed evaluation of SMTP access restriction lists" for a discussion  of
       evaluation context and time.

       The Postfix ETRN implementation accepts only destinations that are eli-
       gible for the Postfix "fast flush" service. See  the  ETRN_README  file
       for details.

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next  line  with  whitespace.   Re-
       strictions are applied in the order as specified; the first restriction
       that matches wins.

       The following restrictions are specific to the domain name  information
       received with the ETRN command.

       check_etrn_access type:table
              Search the specified access database for the ETRN domain name or
              its parent domains. See the access(5) manual page for details.

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

       o      SMTP    command    specific    restrictions    described   under
              smtpd_client_restrictions and smtpd_helo_restrictions.

       Example:

       smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
       What characters are allowed in $name expansions of RBL reply templates.
       Characters  not in the allowed set are replaced by "_".  Use C like es-
       capes to specify special characters such as whitespace.

       The smtpd_expansion_filter value is not subject to  Postfix  configura-
       tion parameter $name expansion.

       This feature is available in Postfix 2.0 and later.

smtpd_forbid_bare_newline (default: Postfix < 3.9: no)
       Reject or restrict input lines from an SMTP client that end in <LF> in-
       stead of the standard <CR><LF>. Such line endings are commonly  allowed
       with  UNIX-based  SMTP servers, but they violate RFC 5321, and allowing
       such line endings can make a server vulnerable to SMTP smuggling.

       Specify one of the following values (case does not matter):

       normalize
              Require the  standard  End-of-DATA  sequence  <CR><LF>.<CR><LF>.
              Otherwise,  allow command or message content lines ending in the
              non-standard <LF>, and process them as if the  client  sent  the
              standard <CR><LF>.
              This  maintains  compatibility  with many legitimate SMTP client
              applications that send a mix of standard and  non-standard  line
              endings,  but will fail to receive email from client implementa-
              tions that do not  terminate  DATA  content  with  the  standard
              End-of-DATA sequence <CR><LF>.<CR><LF>.
              Such  clients can be excluded with smtpd_forbid_bare_newline_ex-
              clusions.

       yes    Compatibility alias for normalize.

       reject Require the standard End-of-DATA sequence <CR><LF>.<CR><LF>. Re-
              ject  a  command  or  message  content when a line contains bare
              <LF>, log a "bare <LF> received" error, and reply with the  SMTP
              status code in $smtpd_forbid_bare_newline_reject_code.
              This will reject email from SMTP clients that send any non-stan-
              dard line endings such as web applications, netcat, or load bal-
              ancer health checks.
              This  will also reject email from services that use BDAT to send
              MIME text containing a bare newline (RFC 3030 Section 3 requires
              canonical  MIME  format  for  text message types, defined in RFC
              2045 Sections 2.7 and 2.8).
              Such clients can be excluded with  smtpd_forbid_bare_newline_ex-
              clusions (or, in the case of BDAT violations, BDAT can be selec-
              tively disabled with smtpd_discard_ehlo_keyword_address_maps, or
              globally disabled with smtpd_discard_ehlo_keywords).

       no (default)
              Do    not    require    the    standard   End-of-DATA   sequence
              <CR><LF>.<CR><LF>. Always process a bare <LF> as if  the  client
              sent <CR><LF>. This option is fully backwards compatible, but is
              not recommended for an Internet-facing SMTP server,  because  it
              is vulnerable to  SMTP smuggling.

       Recommended settings:

           # Require the standard End-of-DATA sequence <CR><LF>.<CR><LF>.
           # Otherwise, allow bare <LF> and process it as if the client sent
           # <CR><LF>.
           #
           # This maintains compatibility with many legitimate SMTP client
           # applications that send a mix of standard and non-standard line
           # endings, but will fail to receive email from client implementations
           # that do not terminate DATA content with the standard End-of-DATA
           # sequence <CR><LF>.<CR><LF>.
           #
           # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
           # The example below allowlists SMTP clients in trusted networks.
           #
           smtpd_forbid_bare_newline = normalize
           smtpd_forbid_bare_newline_exclusions = $mynetworks

       Alternative:

           # Reject input lines that contain <LF> and log a "bare <LF> received"
           # error. Require that input lines end in <CR><LF>, and require the
           # standard End-of-DATA sequence <CR><LF>.<CR><LF>.
           #
           # This will reject email from SMTP clients that send any non-standard
           # line endings such as web applications, netcat, or load balancer
           # health checks.
           #
           # This will also reject email from services that use BDAT to send
           # MIME text containing a bare newline (RFC 3030 Section 3 requires
           # canonical MIME format for text message types, defined in RFC 2045
           # Sections 2.7 and 2.8).
           #
           # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
           # The example below allowlists SMTP clients in trusted networks.
           #
           smtpd_forbid_bare_newline = reject
           smtpd_forbid_bare_newline_exclusions = $mynetworks
           #
           # Alternatively, in the case of BDAT violations, BDAT can be selectively
           # disabled with smtpd_discard_ehlo_keyword_address_maps, or globally
           # disabled with smtpd_discard_ehlo_keywords.
           #
           # smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file
           # /path/to/file:
           #     10.0.0.0/24 chunking, silent-discard
           # smtpd_discard_ehlo_keywords = chunking, silent-discard

       This  feature  with  settings yes and no is available in Postfix 3.8.4,
       3.7.9, 3.6.13, and 3.5.23. Additionally, the settings reject, and  nor-
       malize  are  available  with Postfix >= 3.9, 3.8.5, 3.7.10, 3.6.14, and
       3.5.24.

smtpd_forbid_bare_newline_exclusions (default: $mynetworks)
       Exclude the specified clients from  smtpd_forbid_bare_newline  enforce-
       ment.  This setting uses the same syntax and parent-domain matching be-
       havior as mynetworks.

       This feature is available in Postfix >= 3.9, 3.8.4, 3.7.9, 3.6.13,  and
       3.5.23.

smtpd_forbid_bare_newline_reject_code (default: 550)
       The  numerical  Postfix  SMTP server response code when rejecting a re-
       quest with "smtpd_forbid_bare_newline = reject".  Specify a 5XX  status
       code (521 to disconnect).

       This feature is available in Postfix >= 3.9, 3.8.5, 3.7.10, 3.6.14, and
       3.5.24.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
       List of commands that cause the Postfix SMTP server to immediately ter-
       minate  the  session  with  a  221 code. This can be used to disconnect
       clients that obviously attempt to abuse the system. In addition to  the
       commands  listed  in  this parameter, commands that follow the "Label:"
       format of message headers will also cause a disconnect.

       This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, overload: 1)
       The maximal number of errors a remote SMTP client is  allowed  to  make
       without  delivering  mail. The Postfix SMTP server disconnects when the
       limit is exceeded. Normally the default limit is 20, but it changes un-
       der  overload  to just 1. With Postfix 2.5 and earlier, the SMTP server
       always allows up to 20 errors by default.

smtpd_helo_required (default: no)
       Require that a remote SMTP client introduces itself with  the  HELO  or
       EHLO command before sending the MAIL command or other commands that re-
       quire EHLO negotiation.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the  con-
       text  of  a client HELO command.  See SMTPD_ACCESS_README, section "De-
       layed evaluation of SMTP access restriction lists" for a discussion  of
       evaluation context and time.

       The default is to permit everything.

       Note:  specify  "smtpd_helo_required  =  yes" to fully enforce this re-
       striction (without "smtpd_helo_required = yes",  a  client  can  simply
       skip smtpd_helo_restrictions by not sending HELO or EHLO).

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next  line  with  whitespace.   Re-
       strictions are applied in the order as specified; the first restriction
       that matches wins.

       The following restrictions are specific to the hostname information re-
       ceived with the HELO or EHLO command.

       check_helo_access type:table
              Search  the  specified  access(5)  database for the HELO or EHLO
              hostname or parent domains, and execute  the  corresponding  ac-
              tion.   Note:  specify  "smtpd_helo_required = yes" to fully en-
              force this restriction (without "smtpd_helo_required =  yes",  a
              client  can simply skip check_helo_access by not sending HELO or
              EHLO).

       check_helo_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the HELO or EHLO hostname, and execute the corresponding action.
              Note 1: a result of "OK" is not allowed for safety reasons.  In-
              stead,  use DUNNO in order to exclude specific hosts from black-
              lists.  Note 2: specify "smtpd_helo_required = yes" to fully en-
              force  this  restriction (without "smtpd_helo_required = yes", a
              client can simply skip check_helo_a_access by not  sending  HELO
              or EHLO).  This feature is available in Postfix 3.0 and later.

       check_helo_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              HELO or EHLO hostname, and  execute  the  corresponding  action.
              Note  1: a result of "OK" is not allowed for safety reasons. In-
              stead, use DUNNO in order to exclude specific hosts from  black-
              lists.  Note 2: specify "smtpd_helo_required = yes" to fully en-
              force this restriction (without "smtpd_helo_required =  yes",  a
              client  can simply skip check_helo_mx_access by not sending HELO
              or EHLO).  This feature is available in Postfix 2.1 and later.

       check_helo_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the HELO or EHLO hostname, and execute the corresponding action.
              Note 1: a result of "OK" is not allowed for safety reasons.  In-
              stead,  use DUNNO in order to exclude specific hosts from black-
              lists.  Note 2: specify "smtpd_helo_required = yes" to fully en-
              force  this  restriction (without "smtpd_helo_required = yes", a
              client can simply skip check_helo_ns_access by not sending  HELO
              or EHLO). This feature is available in Postfix 2.1 and later.

       reject_invalid_helo_hostname  (with Postfix < 2.3: reject_invalid_host-
       name)
              Reject the request when the HELO or EHLO hostname is  malformed.
              Note:  specify "smtpd_helo_required = yes" to fully enforce this
              restriction (without "smtpd_helo_required = yes", a  client  can
              simply  skip reject_invalid_helo_hostname by not sending HELO or
              EHLO).
              The invalid_hostname_reject_code specifies the response code for
              rejected requests (default: 501).

       reject_non_fqdn_helo_hostname     (with     Postfix    <    2.3:    re-
       ject_non_fqdn_hostname)
              Reject the request when the HELO or  EHLO  hostname  is  not  in
              fully-qualified  domain  or address literal form, as required by
              the RFC. Note: specify "smtpd_helo_required = yes" to fully  en-
              force  this  restriction (without "smtpd_helo_required = yes", a
              client can  simply  skip  reject_non_fqdn_helo_hostname  by  not
              sending HELO or EHLO).
              The  non_fqdn_reject_code  parameter specifies the response code
              for rejected requests (default: 504).

       reject_rhsbl_helo rbl_domain=d.d.d.d
              Reject the request when the HELO or EHLO hostname is listed with
              the A record "d.d.d.d" under rbl_domain (Postfix version 2.1 and
              later only).  Each "d" is a number, or  a  pattern  inside  "[]"
              that  contains one or more ";"-separated numbers or number..num-
              ber ranges (Postfix version 2.8 and later).  If no "=d.d.d.d" is
              specified,  reject the request when the HELO or EHLO hostname is
              listed  with  any  A  record  under  rbl_domain.  See  the   re-
              ject_rbl_client  description for additional RBL related configu-
              ration parameters.  Note: specify "smtpd_helo_required = yes" to
              fully  enforce  this restriction (without "smtpd_helo_required =
              yes", a client can simply skip reject_rhsbl_helo by not  sending
              HELO  or  EHLO).  This  feature  is available in Postfix 2.0 and
              later.

       reject_unknown_helo_hostname (with Postfix < 2.3:  reject_unknown_host-
       name)
              Reject  the  request when the HELO or EHLO hostname has no DNS A
              or MX record.
              The reply is specified with the unknown_hostname_reject_code pa-
              rameter  (default: 450) or unknown_helo_hostname_tempfail_action
              (default: defer_if_permit).  See the  respective  parameter  de-
              scriptions for details.
              Note:  specify "smtpd_helo_required = yes" to fully enforce this
              restriction (without "smtpd_helo_required = yes", a  client  can
              simply  skip reject_unknown_helo_hostname by not sending HELO or
              EHLO).

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

       o      Client  hostname  or  network  address specific restrictions de-
              scribed under smtpd_client_restrictions.

       o      SMTP   command    specific    restrictions    described    under
              smtpd_sender_restrictions or smtpd_recipient_restrictions.  When
              sender or recipient restrictions are listed under smtpd_helo_re-
              strictions,  they  have  effect  only with "smtpd_delay_reject =
              yes", so that $smtpd_helo_restrictions is evaluated at the  time
              of the RCPT TO command.

       Examples:

       smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
       smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
       The  maximal number of lines in the Postfix SMTP server command history
       before it is flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, overload: 1)
       The number of junk commands (NOOP, VRFY, ETRN or RSET)  that  a  remote
       SMTP client can send before the Postfix SMTP server starts to increment
       the error counter with each junk command.  The junk  command  count  is
       reset after mail is delivered.  See also the smtpd_error_sleep_time and
       smtpd_soft_error_limit configuration parameters.  Normally the  default
       limit is 100, but it changes under overload to just 1. With Postfix 2.5
       and earlier, the SMTP server always allows up to 100 junk  commands  by
       default.

smtpd_log_access_permit_actions (default: empty)
       Enable  logging  of  the  named  "permit" actions in SMTP server access
       lists (by default, the SMTP server logs "reject" actions but not  "per-
       mit"  actions).   This feature does not affect conditional actions such
       as "defer_if_permit".

       Specify a list of "permit" action names, "/file/name"  or  "type:table"
       patterns,  separated  by  commas and/or whitespace. The list is matched
       left to right, and the search stops on the first match. A  "/file/name"
       pattern  is  replaced  by  its contents; a "type:table" lookup table is
       matched when a name matches a lookup key  (the  lookup  result  is  ig-
       nored).  Continue long lines by starting the next line with whitespace.
       Specify "!pattern" to exclude a name from the list.

       Examples:

       /etc/postfix/main.cf:
           # Log all "permit" actions.
           smtpd_log_access_permit_actions = static:all

       /etc/postfix/main.cf:
           # Log "permit_dnswl_client" only.
           smtpd_log_access_permit_actions = permit_dnswl_client

       This feature is available in Postfix 2.10 and later.

smtpd_milter_maps (default: empty)
       Lookup tables with Milter settings per remote SMTP client  IP  address.
       The lookup result overrides the smtpd_milters setting, and has the same
       syntax.

       Note: lookup tables cannot return empty responses. Specify a lookup re-
       sult  of DISABLE (case does not matter) to indicate that Milter support
       should be disabled.

       Example to disable Milters for local clients:

       /etc/postfix/main.cf:
           smtpd_milter_maps = cidr:/etc/postfix/smtpd_milter_map
           smtpd_milters = inet:host:port, { inet:host:port, ... }, ...

       /etc/postfix/smtpd_milter_map:
           # Disable Milters for local clients.
           127.0.0.0/8    DISABLE
           192.168.0.0/16 DISABLE
           ::/64          DISABLE
           2001:db8::/32  DISABLE

       This feature is available in Postfix 3.2 and later.

smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail  that  arrives
       via  the  Postfix smtpd(8) server. Specify space or comma as separator.
       See the MILTER_README document for details.

       This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
       List of commands that the Postfix SMTP server replies to with "250 Ok",
       without  doing any syntax checks and without changing state.  This list
       overrides any commands built into the Postfix SMTP server.

smtpd_null_access_lookup_key (default: <>)
       The lookup key to be used in SMTP access(5) tables instead of the  null
       sender address.

smtpd_peername_lookup (default: yes)
       Attempt to look up the remote SMTP client hostname, and verify that the
       name matches the client IP address. A client name is set  to  "unknown"
       when  it  cannot  be looked up or verified, or when name lookup is dis-
       abled.  Turning off name lookup reduces delays due to  DNS  lookup  and
       increases the maximal inbound delivery rate.

       This feature is available in Postfix 2.3 and later.

smtpd_per_record_deadline (default: normal: no, overload: yes)
       Change  the  behavior  of  the smtpd_timeout and smtpd_starttls_timeout
       time limits, from a time limit per read or write system call, to a time
       limit  to send or receive a complete record (an SMTP command line, SMTP
       response line, SMTP message content line,  or  TLS  protocol  message).
       This limits the impact from hostile peers that trickle data one byte at
       a time.

       Note: when per-record deadlines are enabled, a short timeout may  cause
       problems  with TLS over very slow network connections.  The reasons are
       that a TLS protocol message can be up to 16 kbytes long  (with  TLSv1),
       and that an entire TLS protocol message must be sent or received within
       the per-record deadline.

       This feature is available in Postfix 2.9 and later. With older  Postfix
       releases, the behavior is as if this parameter is set to "no".

smtpd_policy_service_default_action  (default:  451 4.3.5 Server configuration
       problem)
       The default action when an SMTPD policy service request fails.  Specify
       "DUNNO"  to  behave  as if the failed  SMTPD policy service request was
       not sent, and to continue processing other access restrictions, if any.

       Limitations:

       o      This parameter may specify any value that would be a valid SMTPD
              policy server response (or access(5) map lookup result).  An ac-
              cess(5) map or policy server in this parameter value may need to
              be declared in advance with a restriction_class setting.

       o      If the specified action invokes another check_policy_service re-
              quest, that request will have the built-in default action.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_max_idle (default: 300s)
       The time after which an idle SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
       The time after which an  active  SMTPD  policy  service  connection  is
       closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_policy_context (default: empty)
       Optional  information  that  the  Postfix  SMTP server specifies in the
       "policy_context" attribute of a policy service request (originally,  to
       share  the  same  service  endpoint among multiple check_policy_service
       clients).

       This feature is available in Postfix 3.1 and later.

smtpd_policy_service_request_limit (default: 0)
       The maximal number of requests per SMTPD policy service connection,  or
       zero  (no  limit). Once a connection reaches this limit, the connection
       is closed and the next request will be sent over a new connection. This
       is a workaround to avoid error-recovery delays with policy servers that
       cannot maintain a persistent connection.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_retry_delay (default: 1s)
       The delay between attempts to resend a failed SMTPD policy service  re-
       quest. Specify a value greater than zero.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_timeout (default: 100s)
       The time limit for connecting to, writing to, or receiving from a dele-
       gated SMTPD policy server.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_try_limit (default: 2)
       The maximal number of attempts to send an SMTPD policy service  request
       before giving up. Specify a value greater than zero.

       This feature is available in Postfix 3.0 and later.

smtpd_proxy_ehlo (default: $myhostname)
       How  the  Postfix SMTP server announces itself to the proxy filter.  By
       default, the Postfix hostname is used.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
       The hostname and TCP port of the  mail  filtering  proxy  server.   The
       proxy  receives  all mail from the Postfix SMTP server, and is supposed
       to give the result to another Postfix SMTP server process.

       Specify  "host:port"  or  "inet:host:port"  for  a  TCP  endpoint,   or
       "unix:pathname"  for  a UNIX-domain endpoint. The host can be specified
       as an IP address or as a symbolic name; no MX lookups are  done.   When
       no  "host"  or  "host:"   are  specified, the local machine is assumed.
       Pathname interpretation is relative to the Postfix queue directory.

       This feature is available in Postfix 2.1 and later.

       The "inet:" and "unix:" prefixes  are  available  in  Postfix  2.3  and
       later.

smtpd_proxy_options (default: empty)
       List  of  options that control how the Postfix SMTP server communicates
       with a before-queue content filter. Specify zero or more of the follow-
       ing, separated by comma or whitespace.

       speed_adjust
              Do  not connect to a before-queue content filter until an entire
              message has been received. This reduces the number of simultane-
              ous before-queue content filter processes.

       NOTE  1: A filter must not selectively reject recipients of a multi-re-
       cipient message.  Rejecting all recipients is OK, as is  accepting  all
       recipients.

       NOTE  2:  This feature increases the minimum amount of free queue space
       by $message_size_limit. The extra space is needed to save  the  message
       to a temporary file.

       This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)
       The  time limit for connecting to a proxy filter and for sending or re-
       ceiving information.  When a connection fails the client gets a generic
       error  message while more detailed information is logged to the maillog
       file.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
       The  maximal  number of recipients that the Postfix SMTP server accepts
       per message delivery request.

smtpd_recipient_overshoot_limit (default: 1000)
       The number of recipients that a remote SMTP client can send  in  excess
       of  the limit specified with $smtpd_recipient_limit, before the Postfix
       SMTP server increments the per-session error count for each excess  re-
       cipient.

smtpd_recipient_restrictions (default: see postconf -d output)
       Optional  restrictions that the Postfix SMTP server applies in the con-
       text of a client RCPT TO command, after smtpd_relay_restrictions.   See
       SMTPD_ACCESS_README,  section  "Delayed  evaluation  of SMTP access re-
       striction lists" for a discussion of evaluation context and time.

       With Postfix versions before 2.10, the rules for relay  permission  and
       spam blocking were combined under smtpd_recipient_restrictions, result-
       ing in error-prone configuration.  As of Postfix 2.10, relay permission
       rules are preferably implemented with smtpd_relay_restrictions, so that
       a permissive spam blocking  policy  under  smtpd_recipient_restrictions
       will no longer result in a permissive mail relay policy.

       For  backwards  compatibility, sites that migrate from Postfix versions
       before 2.10 can set smtpd_relay_restrictions to the  empty  value,  and
       use smtpd_recipient_restrictions exactly as before.

       IMPORTANT:  Either  the  smtpd_relay_restrictions  or the smtpd_recipi-
       ent_restrictions parameter must specify at least one of  the  following
       restrictions. Otherwise Postfix will refuse to receive mail:

           reject, reject_unauth_destination

           defer, defer_if_permit, defer_unauth_destination

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next  line  with  whitespace.   Re-
       strictions are applied in the order as specified; the first restriction
       that matches wins.

       The following restrictions are specific to the recipient  address  that
       is received with the RCPT TO command.

       check_recipient_access type:table
              Search the specified access(5) database for the resolved RCPT TO
              address, domain, parent domains, or localpart@, and execute  the
              corresponding action.

       check_recipient_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the RCPT TO domain, and execute the corresponding action.  Note:
              a result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 3.0 and later.

       check_recipient_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              RCPT TO domain, and execute the corresponding action.   Note:  a
              result  of  "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 2.1 and later.

       check_recipient_ns_access type:table
              Search  the specified access(5) database for the DNS servers for
              the RCPT TO domain, and execute the corresponding action.  Note:
              a result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 2.1 and later.

       permit_auth_destination
              Permit the request when one of the following is true:

       o      Postfix  is  mail forwarder: the resolved RCPT TO domain matches
              $relay_domains or a subdomain thereof, and the address  contains
              no sender-specified routing (user@elsewhere@domain),

       o      Postfix  is  the  final destination: the resolved RCPT TO domain
              matches  $mydestination,  $inet_interfaces,   $proxy_interfaces,
              $virtual_alias_domains, or $virtual_mailbox_domains, and the ad-
              dress contains no sender-specified  routing  (user@elsewhere@do-
              main).

       permit_mx_backup
              Permit  the  request when the local mail system is backup MX for
              the RCPT TO domain, or when the domain is an authorized destina-
              tion (see permit_auth_destination for definition).

       o      Safety:  permit_mx_backup  does  not  accept addresses that have
              sender-specified  routing   information   (example:   user@else-
              where@domain).

       o      Safety:  permit_mx_backup  can be vulnerable to mis-use when ac-
              cess is not restricted with permit_mx_backup_networks.

       o      Safety: as of Postfix version 2.3,  permit_mx_backup  no  longer
              accepts the address when the local mail system is primary MX for
              the recipient domain.  Exception: permit_mx_backup  accepts  the
              address  when  it  specifies an authorized destination (see per-
              mit_auth_destination for definition).

       o      Limitation: mail may be rejected in  case  of  a  temporary  DNS
              lookup problem with Postfix prior to version 2.0.

       reject_non_fqdn_recipient
              Reject  the  request when the RCPT TO address specifies a domain
              that is not in fully-qualified domain form, as required  by  the
              RFC.
              The  non_fqdn_reject_code  parameter specifies the response code
              for rejected requests (default: 504).

       reject_rhsbl_recipient rbl_domain=d.d.d.d
              Reject the request when the RCPT TO domain is listed with the  A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
              only).  Each "d" is a number, or a pattern inside "[]" that con-
              tains one or more ";"-separated numbers or number..number ranges
              (Postfix version 2.8 and later). If no "=d.d.d.d" is  specified,
              reject  the request when the RCPT TO domain is listed with any A
              record under rbl_domain.
              The maps_rbl_reject_code parameter specifies the  response  code
              for  rejected requests (default: 554); the default_rbl_reply pa-
              rameter specifies the default  server  reply;  and  the  rbl_re-
              ply_maps  parameter specifies tables with server replies indexed
              by rbl_domain.  This feature is available in Postfix version 2.0
              and later.

       reject_unauth_destination
              Reject the request unless one of the following is true:

       o      Postfix  is  mail forwarder: the resolved RCPT TO domain matches
              $relay_domains  or  a  subdomain  thereof,   and   contains   no
              sender-specified routing (user@elsewhere@domain),

       o      Postfix  is  the  final destination: the resolved RCPT TO domain
              matches  $mydestination,  $inet_interfaces,   $proxy_interfaces,
              $virtual_alias_domains,  or  $virtual_mailbox_domains,  and con-
              tains no sender-specified routing (user@elsewhere@domain).
              The relay_domains_reject_code parameter specifies  the  response
              code for rejected requests (default: 554).

       defer_unauth_destination
              Reject  the  same  requests as reject_unauth_destination, with a
              non-permanent error code.  This feature is available in  Postfix
              2.10 and later.

       reject_unknown_recipient_domain
              Reject the request when Postfix is not final destination for the
              recipient domain, and the RCPT TO domain has 1) no DNS MX and no
              DNS A record or 2) a malformed MX record such as a record with a
              zero-length MX hostname (Postfix version 2.3 and later).
              The reply is specified with the unknown_address_reject_code  pa-
              rameter  (default:  450),  unknown_address_tempfail_action  (de-
              fault: defer_if_permit), or 556 (nullmx, Postfix 3.0 and later).
              See the respective parameter descriptions for details.

       reject_unlisted_recipient  (with  Postfix  version  2.0:  check_recipi-
       ent_maps)
              Reject the request when the RCPT TO address is not listed in the
              list of valid recipients for its domain class. See the smtpd_re-
              ject_unlisted_recipient parameter description for details.  This
              feature is available in Postfix 2.1 and later.

       reject_unverified_recipient
              Reject  the request when mail to the RCPT TO address is known to
              bounce, or when the recipient address destination is not  reach-
              able.   Address  verification information is managed by the ver-
              ify(8) server; see the ADDRESS_VERIFICATION_README file for  de-
              tails.
              The unverified_recipient_reject_code parameter specifies the nu-
              merical response code when an address is known  to  bounce  (de-
              fault:  450,  change  into 550 when you are confident that it is
              safe to do so).
              The unverified_recipient_defer_code parameter specifies the  nu-
              merical response code when an address probe failed due to a tem-
              porary problem (default: 450).
              The unverified_recipient_tempfail_action parameter specifies the
              action  after  address  probe failure due to a temporary problem
              (default: defer_if_permit).
              This feature breaks for aliased  addresses  with  "enable_origi-
              nal_recipient = no" (Postfix <= 3.2).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       o      Generic  restrictions  that can be used in any SMTP command con-
              text, described under smtpd_client_restrictions.

       o      SMTP   command    specific    restrictions    described    under
              smtpd_client_restrictions,      smtpd_helo_restrictions      and
              smtpd_sender_restrictions.

       Example:

       # The Postfix before 2.10 default mail relay policy. Later Postfix
       # versions implement this preferably with smtpd_relay_restrictions.
       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_footer (default: empty)
       Optional information that is appended after each  Postfix  SMTP  server
       4XX or 5XX response.

       The following example uses "\c" at the start of the template (supported
       in Postfix 2.10 and later) to suppress the line break between the reply
       text  and  the  footer  text. With earlier Postfix versions, the footer
       text always begins on a new line, and the "\c" is output literally.

       /etc/postfix/main.cf:
           smtpd_reject_footer = \c. For assistance, call 800-555-0101.
            Please provide the following information in your problem report:
            time ($localtime), client ($client_address) and server
            ($server_name).

       Server response:

           550-5.5.1 <user@example> Recipient address rejected: User
           unknown. For assistance, call 800-555-0101. Please provide the
           following information in your problem report: time (Jan 4 15:42:00),
           client (192.168.1.248) and server (mail1.example.com).

       Note: the above text is meant to make it easier  to  find  the  Postfix
       logfile  records  for  a  failed  SMTP  session. The text itself is not
       logged to the Postfix SMTP server's maillog file.

       Be sure to keep the text as short as possible. Long text may  be  trun-
       cated  before it is logged to the remote SMTP client's maillog file, or
       before it is returned to the sender in a delivery status notification.

       The template text is not subject  to  Postfix  configuration  parameter
       $name  expansion.  Instead,  this  feature supports a limited number of
       $name attributes in the footer text. These attributes are replaced with
       their current value for the SMTP session.

       Note:  specify  $$name in footer text that is looked up from regexp: or
       pcre:-based smtpd_reject_footer_maps, otherwise the Postfix server will
       not use the footer text and will log a warning instead.

       client_address
              The Client IP address that is logged in the maillog file.

       client_port
              The client TCP port that is logged in the maillog file.

       localtime
              The  server  local  time (Mmm dd hh:mm:ss) that is logged in the
              maillog file.

       server_name
              The server's myhostname value.  This attribute is made available
              for  sites  with multiple MTAs (perhaps behind a load-balancer),
              where the server name  can  help  the  server  support  team  to
              quickly find the right log files.

       Notes:

       o      NOT SUPPORTED are other attributes such as sender, recipient, or
              main.cf parameters.

       o      For safety reasons,  text  that  does  not  match  $smtpd_expan-
              sion_filter is censored.

       This  feature supports the two-character sequence \n as a request for a
       line break in the footer text. Postfix automatically inserts after each
       line  break the three-digit SMTP reply code (and optional enhanced sta-
       tus code) from the original Postfix reject message.

       To work around mail software that mis-handles multi-line replies, spec-
       ify  the  two-character sequence \c at the start of the template.  This
       suppresses the line break between the reply text and  the  footer  text
       (Postfix 2.10 and later).

       This feature is available in Postfix 2.8 and later.

smtpd_reject_footer_maps (default: empty)
       Lookup  tables,  indexed by the complete Postfix SMTP server 4xx or 5xx
       response, with reject footer templates. See smtpd_reject_footer for de-
       tails.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       This feature is available in Postfix 3.4 and later.

smtpd_reject_unlisted_recipient (default: yes)
       Request that the Postfix SMTP server rejects mail for unknown recipient
       addresses, even when no explicit reject_unlisted_recipient  access  re-
       striction is specified. This prevents the Postfix queue from filling up
       with undeliverable MAILER-DAEMON messages.

       An address is always considered "known" when it  matches  a  virtual(5)
       alias or a canonical(5) mapping.

       o      The recipient domain matches $mydestination, $inet_interfaces or
              $proxy_interfaces, but the recipient is not listed in $local_re-
              cipient_maps, and $local_recipient_maps is not null.

       o      The  recipient domain matches $virtual_alias_domains but the re-
              cipient is not listed in $virtual_alias_maps.

       o      The recipient domain matches  $virtual_mailbox_domains  but  the
              recipient  is  not  listed  in  $virtual_mailbox_maps, and $vir-
              tual_mailbox_maps is not null.

       o      The recipient domain matches $relay_domains but the recipient is
              not  listed  in $relay_recipient_maps, and $relay_recipient_maps
              is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
       Request that the Postfix SMTP server rejects mail from  unknown  sender
       addresses, even when no explicit reject_unlisted_sender access restric-
       tion is specified. This can slow down an explosion of forged mail  from
       worms or viruses.

       An  address  is  always considered "known" when it matches a virtual(5)
       alias or a canonical(5) mapping.

       o      The sender domain matches  $mydestination,  $inet_interfaces  or
              $proxy_interfaces, but the sender is not listed in $local_recip-
              ient_maps, and $local_recipient_maps is not null.

       o      The sender domain matches $virtual_alias_domains but the  sender
              is not listed in $virtual_alias_maps.

       o      The  sender  domain  matches  $virtual_mailbox_domains  but  the
              sender  is  not  listed  in  $virtual_mailbox_maps,  and   $vir-
              tual_mailbox_maps is not null.

       o      The  sender  domain matches $relay_domains but the sender is not
              listed in $relay_recipient_maps,  and  $relay_recipient_maps  is
              not null.

       This feature is available in Postfix 2.1 and later.

smtpd_relay_restrictions  (default:  permit_mynetworks,  permit_sasl_authenti-
       cated, defer_unauth_destination)
       Access restrictions for mail relay control that the Postfix SMTP server
       applies  in  the  context  of the RCPT TO command, before smtpd_recipi-
       ent_restrictions.  See SMTPD_ACCESS_README, section "Delayed evaluation
       of  SMTP  access restriction lists" for a discussion of evaluation con-
       text and time.

       With Postfix versions before 2.10, the rules for relay  permission  and
       spam blocking were combined under smtpd_recipient_restrictions, result-
       ing in error-prone configuration.  As of Postfix 2.10, relay permission
       rules are preferably implemented with smtpd_relay_restrictions, so that
       a permissive spam blocking  policy  under  smtpd_recipient_restrictions
       will no longer result in a permissive mail relay policy.

       For  backwards  compatibility, sites that migrate from Postfix versions
       before 2.10 can set smtpd_relay_restrictions to the  empty  value,  and
       use smtpd_recipient_restrictions exactly as before.

       By default, the Postfix SMTP server accepts:

       o      Mail from clients whose IP address matches $mynetworks, or:

       o      Mail  to  remote  destinations that match $relay_domains, except
              for addresses that contain sender-specified routing  (user@else-
              where@domain), or:

       o      Mail  to  local  destinations  that  match  $inet_interfaces  or
              $proxy_interfaces,  $mydestination,  $virtual_alias_domains,  or
              $virtual_mailbox_domains.

       IMPORTANT:  Either  the  smtpd_relay_restrictions  or the smtpd_recipi-
       ent_restrictions parameter must specify at least one of  the  following
       restrictions. Otherwise Postfix will refuse to receive mail:

           reject, reject_unauth_destination

           defer, defer_if_permit, defer_unauth_destination

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next  line  with  whitespace.   The
       same restrictions are available as documented under smtpd_recipient_re-
       strictions.

       This feature is available in Postix 2.10 and later.

smtpd_restriction_classes (default: empty)
       User-defined aliases for groups of access restrictions. The aliases can
       be   specified   in   smtpd_recipient_restrictions  etc.,  and  on  the
       right-hand side of a Postfix access(5) table.

       One major application is for implementing  per-recipient  UCE  control.
       See the RESTRICTION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
       The  application name that the Postfix SMTP server uses for SASL server
       initialization. This controls the name of the SASL configuration  file.
       The  default value is smtpd, corresponding to a SASL configuration file
       named smtpd.conf.

       This feature is available in Postfix 2.1 and 2.2. With Postfix  2.3  it
       was renamed to smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
       Enable  SASL authentication in the Postfix SMTP server. By default, the
       Postfix SMTP server does not use authentication.

       If a remote SMTP client is authenticated, the permit_sasl_authenticated
       access restriction can be used to permit relay access, like this:

           # With Postfix 2.10 and later, the mail relay policy is
           # preferably specified under smtpd_relay_restrictions.
           smtpd_relay_restrictions =
               permit_mynetworks, permit_sasl_authenticated, ...

       # With Postfix before 2.10, the relay policy can be
       # specified only under smtpd_recipient_restrictions.
       smtpd_recipient_restrictions =
           permit_mynetworks, permit_sasl_authenticated, ...

       To  reject  all  SMTP connections from unauthenticated clients, specify
       "smtpd_delay_reject = yes" (which is the default) and use:

           smtpd_client_restrictions = permit_sasl_authenticated, reject

       See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
       Report the SASL authenticated user name in the smtpd(8)  Received  mes-
       sage header.

       This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
       What  remote  SMTP  clients the Postfix SMTP server will not offer AUTH
       support to.

       Some clients (Netscape 4 at least) have a bug that causes them  to  re-
       quire  a login and password whenever AUTH is offered, whether it's nec-
       essary or not. To work around this, specify, for  example,  $mynetworks
       to prevent Postfix from offering AUTH to local clients.

       Specify  a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the  network  part
       of  a host address. You can also "/file/name" or "type:table" patterns.
       A "/file/name" pattern is replaced  by  its  contents;  a  "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).  Continue long lines by  starting  the  next
       line  with whitespace. Specify "!pattern" to exclude an address or net-
       work block from the list.  The form "!/file/name" is supported only  in
       Postfix version 2.4 and later.

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_sasl_exceptions_networks value, and in files  specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

       Example:

       smtpd_sasl_exceptions_networks = $mynetworks

       This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
       The name of the Postfix SMTP server's local SASL authentication realm.

       By default, the local authentication realm name is the null string.

       Examples:

       smtpd_sasl_local_domain = $mydomain
       smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
       Implementation-specific information that the Postfix SMTP server passes
       through  to  the  SASL  plug-in  implementation  that  is selected with
       smtpd_sasl_type.  Typically this specifies the name of a  configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later. In earlier releases
       it was called smtpd_sasl_application_name.

smtpd_sasl_response_limit (default: 12288)
       The maximum length of a SASL client's response to a  server  challenge.
       When  the  client's  "initial response" is longer than the normal limit
       for SMTP commands, the client must omit its initial response, and  wait
       for  an  empty  server challenge; it can then send what would have been
       its "initial response" as a response to  the  empty  server  challenge.
       RFC4954  requires  the server to accept client responses up to at least
       12288 octets of base64-encoded text.  The default  value  is  therefore
       also the minimum value accepted for this parameter.

       This  feature is available in Postfix 3.4 and later. Prior versions use
       "line_length_limit", which may need to be raised to accommodate  larger
       client  responses,  as may be needed with GSSAPI authentication of Win-
       dows AD users who are members of many groups.

smtpd_sasl_security_options (default: noanonymous)
       Postfix SMTP server SASL security options; as of Postfix 2.3  the  list
       of available features depends on the SASL server implementation that is
       selected with smtpd_sasl_type.

       The following security features are defined for the cyrus  server  SASL
       implementation:

       Restrict  what  authentication  mechanisms the Postfix SMTP server will
       offer to the client.  The list of available  authentication  mechanisms
       is system dependent.

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       forward_secrecy
              Only allow methods that support forward secrecy (Dovecot only).

       mutual_auth
              Only  allow  methods  that  provide  mutual  authentication (not
              available with Cyrus SASL version 1).

       By default, the Postfix SMTP server accepts plaintext passwords but not
       anonymous logins.

       Warning:  it appears that clients try authentication methods in the or-
       der as advertised by the server (e.g., PLAIN ANONYMOUS CRAM-MD5)  which
       means  that  if  you  disable  plaintext passwords, clients will log in
       anonymously, even when they should be able to use CRAM-MD5.  So, if you
       disable plaintext logins, disable anonymous logins too.  Postfix treats
       anonymous login as no authentication.

       Example:

       smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_service (default: smtp)
       The service name that is passed to the SASL plug-in  that  is  selected
       with smtpd_sasl_type and smtpd_sasl_path.

       This feature is available in Postfix 2.11 and later. Prior versions be-
       have as if "smtp" is specified.

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
       The SASL authentication security options that the Postfix  SMTP  server
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
       The  SASL  plug-in type that the Postfix SMTP server should use for au-
       thentication. The available types are listed  with  the  "postconf  -a"
       command.

       This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
       Optional  lookup  table  with  the SASL login names that own the sender
       (MAIL FROM) addresses.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.  With lookups from indexed files such as DB or DBM,  or  from
       networked  tables such as NIS, LDAP or SQL, the following search opera-
       tions are done with a sender address of user@domain:

       1) user@domain
              This table lookup is always done and has the highest precedence.

       2) user
              This table lookup is done only  when  the  domain  part  of  the
              sender  address  matches $myorigin, $mydestination, $inet_inter-
              faces or $proxy_interfaces.

       3) @domain
              This table lookup is done last and has the lowest precedence.

       In all cases the result of table lookup must be either "not found" or a
       list of SASL login names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
       Optional  restrictions that the Postfix SMTP server applies in the con-
       text of a client MAIL FROM command.  See  SMTPD_ACCESS_README,  section
       "Delayed  evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to permit everything.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue  long  lines  by  starting the next line with whitespace.  Re-
       strictions are applied in the order as specified; the first restriction
       that matches wins.

       The  following restrictions are specific to the sender address received
       with the MAIL FROM command.

       check_sender_access type:table
              Search the specified access(5) database for the  MAIL  FROM  ad-
              dress,  domain,  parent  domains, or localpart@, and execute the
              corresponding action.

       check_sender_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the  MAIL  FROM  domain,  and  execute the corresponding action.
              Note: a result of "OK" is not allowed for  safety  reasons.  In-
              stead,  use DUNNO in order to exclude specific hosts from black-
              lists.  This feature is available in Postfix 3.0 and later.

       check_sender_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              MAIL FROM domain, and execute the corresponding action.  Note: a
              result of "OK" is not allowed for safety reasons.  Instead,  use
              DUNNO  in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.1 and later.

       check_sender_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the  MAIL  FROM  domain,  and  execute the corresponding action.
              Note: a result of "OK" is not allowed for  safety  reasons.  In-
              stead,  use DUNNO in order to exclude specific hosts from black-
              lists.  This feature is available in Postfix 2.1 and later.

       reject_authenticated_sender_login_mismatch
              Enforces the reject_sender_login_mismatch  restriction  for  au-
              thenticated  clients  only. This feature is available in Postfix
              version 2.1 and later.

       reject_known_sender_login_mismatch
              Apply the reject_sender_login_mismatch restriction only to  MAIL
              FROM addresses that are known in $smtpd_sender_login_maps.  This
              feature is available in Postfix version 2.11 and later.

       reject_non_fqdn_sender
              Reject the request when the MAIL FROM address specifies a domain
              that  is  not  in fully-qualified domain form as required by the
              RFC.
              The non_fqdn_reject_code parameter specifies the  response  code
              for rejected requests (default: 504).

       reject_rhsbl_sender rbl_domain=d.d.d.d
              Reject  the request when the MAIL FROM domain is listed with the
              A record "d.d.d.d" under rbl_domain  (Postfix  version  2.1  and
              later  only).   Each  "d"  is a number, or a pattern inside "[]"
              that contains one or more ";"-separated numbers or  number..num-
              ber  ranges (Postfix version 2.8 and later). If no "=d.d.d.d" is
              specified, reject the request  when  the  MAIL  FROM  domain  is
              listed with any A record under rbl_domain.
              The  maps_rbl_reject_code  parameter specifies the response code
              for rejected requests (default:  554); the default_rbl_reply pa-
              rameter  specifies  the  default  server  reply; and the rbl_re-
              ply_maps parameter specifies tables with server replies  indexed
              by  rbl_domain.   This  feature  is available in Postfix 2.0 and
              later.

       reject_sender_login_mismatch
              Reject the request when  $smtpd_sender_login_maps  specifies  an
              owner  for  the  MAIL FROM address, but the client is not (SASL)
              logged in as that MAIL FROM address owner; or when the client is
              (SASL) logged in, but the client login name doesn't own the MAIL
              FROM address according to $smtpd_sender_login_maps.

       reject_unauthenticated_sender_login_mismatch
              Enforces the reject_sender_login_mismatch restriction for  unau-
              thenticated  clients  only. This feature is available in Postfix
              version 2.1 and later.

       reject_unknown_sender_domain
              Reject the request when Postfix is not final destination for the
              sender address, and the MAIL FROM domain has 1) no DNS MX and no
              DNS A record, or 2) a malformed MX record such as a record  with
              a zero-length MX hostname (Postfix version 2.3 and later).
              The  reply is specified with the unknown_address_reject_code pa-
              rameter  (default:  450),  unknown_address_tempfail_action  (de-
              fault: defer_if_permit), or 550 (nullmx, Postfix 3.0 and later).
              See the respective parameter descriptions for details.

       reject_unlisted_sender
              Reject the request when the MAIL FROM address is not  listed  in
              the  list  of  valid  recipients  for  its domain class. See the
              smtpd_reject_unlisted_sender parameter description for  details.
              This feature is available in Postfix 2.1 and later.

       reject_unverified_sender
              Reject  the  request when mail to the MAIL FROM address is known
              to bounce, or when the sender address destination is not  reach-
              able.   Address  verification information is managed by the ver-
              ify(8) server; see the ADDRESS_VERIFICATION_README file for  de-
              tails.
              The unverified_sender_reject_code parameter specifies the numer-
              ical response code when an address is known to bounce  (default:
              450,  change  into 550 when you are confident that it is safe to
              do so).
              The unverified_sender_defer_code  specifies  the  numerical  re-
              sponse  code  when  an  address  probe failed due to a temporary
              problem (default: 450).
              The unverified_sender_tempfail_action  parameter  specifies  the
              action  after  address  probe failure due to a temporary problem
              (default: defer_if_permit).
              This feature breaks for aliased  addresses  with  "enable_origi-
              nal_recipient = no" (Postfix <= 3.2).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       o      Generic  restrictions  that can be used in any SMTP command con-
              text, described under smtpd_client_restrictions.

       o      SMTP   command    specific    restrictions    described    under
              smtpd_client_restrictions and smtpd_helo_restrictions.

       o      SMTP command specific restrictions described under smtpd_recipi-
              ent_restrictions. When recipient restrictions are  listed  under
              smtpd_sender_restrictions, they have effect only with "smtpd_de-
              lay_reject = yes", so that $smtpd_sender_restrictions is  evalu-
              ated at the time of the RCPT TO command.

       Examples:

       smtpd_sender_restrictions = reject_unknown_sender_domain
       smtpd_sender_restrictions = reject_unknown_sender_domain,
           check_sender_access hash:/etc/postfix/access

smtpd_service_name (default: smtpd)
       The  internal  service that postscreen(8) hands off allowed connections
       to. In a future version there may be different classes of SMTP service.

       This feature is available in Postfix 2.8.

smtpd_soft_error_limit (default: 10)
       The number of errors a remote SMTP client is allowed  to  make  without
       delivering  mail  before the Postfix SMTP server slows down all its re-
       sponses.

       o      With Postfix version 2.1 and later, the Postfix SMTP server  de-
              lays all responses by $smtpd_error_sleep_time seconds.

       o      With  Postfix  versions 2.0 and earlier, the Postfix SMTP server
              delays all responses by (number of errors) seconds.

smtpd_starttls_timeout (default: see postconf -d output)
       The time limit for Postfix SMTP server write and read operations during
       TLS  startup  and  shutdown  handshake  procedures. The current default
       value is stress-dependent. Before Postfix version 2.8, it was fixed  at
       300s.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, overload: 10s)
       The  time  limit for sending a Postfix SMTP server response and for re-
       ceiving a remote SMTP client request. Normally  the  default  limit  is
       300s,  but  it changes under overload to just 10s. With Postfix 2.5 and
       earlier, the SMTP server always uses a time limit of 300s by default.

       Note: if you set SMTP time limits to very large values you may have  to
       update the global ipc_timeout parameter.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtpd_tls_CAfile (default: empty)
       A file containing (PEM format) CA certificates of root CAs  trusted  to
       sign either remote SMTP client certificates or intermediate CA certifi-
       cates.  These are loaded into memory before the smtpd(8) server  enters
       the  chroot jail. If the number of trusted roots is large, consider us-
       ing smtpd_tls_CApath instead, but note that the latter  directory  must
       be  present in the chroot jail if the smtpd(8) server is chrooted. This
       file may also be used to augment the server  certificate  trust  chain,
       but it is best to include all the required certificates directly in the
       server certificate file.

       Specify "smtpd_tls_CAfile = /path/to/system_CA_file" to  use  ONLY  the
       system-supplied default Certification Authority certificates.

       Specify  "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       By default (see smtpd_tls_ask_ccert), client certificates are  not  re-
       quested,  and  smtpd_tls_CAfile should remain empty. If you do make use
       of client certificates, the distinguished names (DNs) of the Certifica-
       tion Authorities listed in smtpd_tls_CAfile are sent to the remote SMTP
       client in the client certificate request message.  MUAs  with  multiple
       client certificates may use the list of preferred Certification Author-
       ities to select the correct client certificate.  You may  want  to  put
       your  "preferred" CA or CAs in this file, and install other trusted CAs
       in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
       A directory containing (PEM format) CA certificates of root CAs trusted
       to  sign either remote SMTP client certificates or intermediate CA cer-
       tificates. Do not forget to create the necessary "hash" links with, for
       example,   "$OPENSSL_HOME/bin/c_rehash   /etc/postfix/certs".   To  use
       smtpd_tls_CApath in chroot mode, this directory (or a copy) must be in-
       side the chroot jail.

       Specify  "smtpd_tls_CApath  = /path/to/system_CA_directory" to use ONLY
       the system-supplied default Certification Authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from  appending
       the system-supplied default CAs and trusting third-party certificates.

       By  default  (see smtpd_tls_ask_ccert), client certificates are not re-
       quested, and smtpd_tls_CApath  should  remain  empty.  In  contrast  to
       smtpd_tls_CAfile,   DNs   of  Certification  Authorities  installed  in
       $smtpd_tls_CApath are not included in the  client  certificate  request
       message.  MUAs  with  multiple  client certificates may use the list of
       preferred Certification Authorities to select the correct  client  cer-
       tificate.   You  may  want  to  put  your  "preferred"  CA  or  CAs  in
       $smtpd_tls_CAfile,  and  install   the   remaining   trusted   CAs   in
       $smtpd_tls_CApath.

       Example:

       smtpd_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
       Force  the Postfix SMTP server to issue a TLS session id, even when TLS
       session caching  is  turned  off  (smtpd_tls_session_cache_database  is
       empty). This behavior is compatible with Postfix < 2.3.

       With  Postfix 2.3 and later the Postfix SMTP server can disable session
       id generation when TLS session caching is turned off. This keeps remote
       SMTP  clients  from  caching  sessions  that almost certainly cannot be
       re-used.

       By default, the Postfix SMTP server always generates TLS  session  ids.
       This works around a known defect in mail client applications such as MS
       Outlook, and may also prevent interoperability issues with other MTAs.

       Example:

       smtpd_tls_always_issue_session_ids = no

       This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
       Ask a remote SMTP client for a client certificate. This information  is
       needed  for certificate based mail relaying with, for example, the per-
       mit_tls_clientcerts feature.

       Some clients such as Netscape will either complain if no certificate is
       available (for the list of CAs in $smtpd_tls_CAfile) or will offer mul-
       tiple client certificates to choose from. This may be annoying, so this
       option is "off" by default.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
       When  TLS encryption is optional in the Postfix SMTP server, do not an-
       nounce or accept SASL authentication over unencrypted connections.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)
       The verification depth for remote SMTP client certificates. A depth  of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The  default verification depth is 9 (the OpenSSL default) for compati-
       bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
       value  was  5, but the limit was not actually enforced. If you have set
       this to a lower  non-default  value,  certificates  with  longer  trust
       chains  may  now fail to verify. Certificate chains with 1 or 2 CAs are
       common, deeper chains are more rare and any  number  between  5  and  9
       should suffice in practice. You can choose a lower number if, for exam-
       ple, you trust certificates directly signed by an issuing  CA  but  not
       any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
       File  with the Postfix SMTP server RSA certificate in PEM format.  This
       file may also contain the Postfix SMTP server private  RSA  key.   With
       Postfix  >= 3.4 the preferred way to configure server keys and certifi-
       cates is via the "smtpd_tls_chain_files" parameter.

       Public Internet MX hosts without certificates signed by  a  "reputable"
       CA  must  generate,  and  be  prepared  to  present  to most clients, a
       self-signed or private-CA signed certificate. The client  will  not  be
       able  to  authenticate the server, but unless it is running Postfix 2.3
       or similar software, it will still insist on a server certificate.

       For servers that are not public Internet  MX  hosts,  Postfix  supports
       configurations  with  no certificates. This entails the use of just the
       anonymous TLS ciphers, which are not supported by typical SMTP clients.
       Since  some  clients  may not fall back to plain text after a TLS hand-
       shake failure, a certificate-less Postfix SMTP server will be unable to
       receive  email  from some TLS-enabled clients. To avoid accidental con-
       figurations with no certificates, Postfix enables certificate-less  op-
       eration     only     when    the    administrator    explicitly    sets
       "smtpd_tls_cert_file = none". This ensures that new Postfix SMTP server
       configurations will not accidentally enable TLS without certificates.

       Note that server certificates are not optional in TLS 1.3. To run with-
       out certificates you'd have to disable the TLS 1.3 protocol by  includ-
       ing    '!TLSv1.3'    in    "smtpd_tls_protocols"   and   perhaps   also
       "smtpd_tls_mandatory_protocols".  It is simpler instead to just config-
       ure  a  certificate  chain.   Certificate-less  operation is not recom-
       mended.

       Both RSA and DSA certificates  are  supported.   When  both  types  are
       present, the cipher used determines which certificate will be presented
       to the client.  For Netscape and OpenSSL clients without special cipher
       choices the RSA certificate is preferred.

       To  enable  a remote SMTP client to verify the Postfix SMTP server cer-
       tificate, the issuing CA certificates must be  made  available  to  the
       client. You should include the required certificates in the server cer-
       tificate file, the server certificate first,  then  the  issuing  CA(s)
       (bottom-up order).

       Example: the certificate for "server.example.com" was issued by "inter-
       mediate CA" which itself has a certificate of "root  CA".   Create  the
       server.pem   file   with   "cat   server_cert.pem   intermediate_CA.pem
       root_CA.pem > server.pem".

       If you also want to verify client certificates issued by these CAs, you
       can  add  the CA certificates to the smtpd_tls_CAfile, in which case it
       is  not  necessary   to   have   them   in   the   smtpd_tls_cert_file,
       smtpd_tls_dcert_file (obsolete) or smtpd_tls_eccert_file.

       A certificate supplied here must be usable as an SSL server certificate
       and hence pass the "openssl verify -purpose sslserver ..." test.

       Example:

       smtpd_tls_cert_file = /etc/postfix/server.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_chain_files (default: empty)
       List of one or more PEM files, each holding one or  more  private  keys
       directly followed by a corresponding certificate chain.  The file names
       are separated by commas and/or whitespace.   This  parameter  obsoletes
       the  legacy algorithm-specific key and certificate file settings.  When
       this parameter is non-empty, the legacy parameters are ignored,  and  a
       warning is logged if any are also non-empty.

       With  the proliferation of multiple private key algorithms-which, as of
       OpenSSL 1.1.1, include DSA (obsolete), RSA, ECDSA, Ed25519 and Ed448-it
       is increasingly impractical to use separate parameters to configure the
       key and certificate chain for each algorithm.  Therefore,  Postfix  now
       supports  storing multiple keys and corresponding certificate chains in
       a single file or in a set of files.

       Each key must appear immediately before the corresponding  certificate,
       optionally followed by additional issuer certificates that complete the
       certificate chain for that key.  When  multiple  files  are  specified,
       they  are  equivalent  to a single file that is concatenated from those
       files in the given order.  Thus, while a key must  always  precede  its
       certificate  and issuer chain, it can be in a separate file, so long as
       that file is listed immediately before the file that holds  the  corre-
       sponding  certificate  chain.  Once all the files are concatenated, the
       sequence of PEM objects must be: key1, cert1,  [chain1],  key2,  cert2,
       [chain2], ..., keyN, certN, [chainN].

       Storing  the private key in the same file as the corresponding certifi-
       cate is more reliable.  With the key and certificate in separate files,
       there is a chance that during key rollover a Postfix process might load
       a private key and certificate from separate  files  that  don't  match.
       Various  operational errors may even result in a persistent broken con-
       figuration in which the certificate does not match the private key.

       The file or files must contain at most one key of each type.   If,  for
       example,  two or more RSA keys and corresponding chains are listed, de-
       pending on the version of OpenSSL either only the last one will be used
       or  an  configuration error may be detected.  Note that while "Ed25519"
       and "Ed448" are  considered  separate  algorithms,  the  various  ECDSA
       curves  (typically  one of prime256v1, secp384r1 or secp521r1) are con-
       sidered as different parameters of a single "ECDSA" algorithm, so it is
       not presently possible to configure keys for more than one ECDSA curve.

       RSA  is  still  the  most  widely supported algorithm.  Presently (late
       2018), ECDSA support is common, but not yet universal, and Ed25519  and
       Ed448 support is mostly absent.  Therefore, an RSA key should generally
       be configured, along with any additional keys for the other  algorithms
       when desired.

       Example  (separate  files  for  each  key and corresponding certificate
       chain):

           /etc/postfix/main.cf:
               smtpd_tls_chain_files =
                   ${config_directory}/ed25519.pem,
                   ${config_directory}/ed448.pem,
                   ${config_directory}/rsa.pem

           /etc/postfix/ed25519.pem:
               -----BEGIN PRIVATE KEY-----
               MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
               ...
               nC0egv51YPDWxEHom4QA
               -----END CERTIFICATE-----

           /etc/postfix/ed448.pem:
               -----BEGIN PRIVATE KEY-----
               MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
               LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
               ...
               pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
               -----END CERTIFICATE-----

           /etc/postfix/rsa.pem:
               -----BEGIN PRIVATE KEY-----
               MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
               ...
               ahQkZ3+krcaJvDSMgvu0tDc=
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
               ...
               Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
               -----END CERTIFICATE-----

       Example (all keys and certificates in a single file):

           /etc/postfix/main.cf:
               smtpd_tls_chain_files = ${config_directory}/chains.pem

           /etc/postfix/chains.pem:
               -----BEGIN PRIVATE KEY-----
               MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
               ...
               nC0egv51YPDWxEHom4QA
               -----END CERTIFICATE-----
               -----BEGIN PRIVATE KEY-----
               MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
               LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
               ...
               pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
               -----END CERTIFICATE-----
               -----BEGIN PRIVATE KEY-----
               MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
               ...
               ahQkZ3+krcaJvDSMgvu0tDc=
               -----END PRIVATE KEY-----
               -----BEGIN CERTIFICATE-----
               MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
               ...
               Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
               -----END CERTIFICATE-----

       This feature is available in Postfix 3.4 and later.

smtpd_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP server  TLS  cipher
       list.  It  is  easy  to  create interoperability problems by choosing a
       non-default cipher list. Do not use a non-default TLS cipherlist for MX
       hosts on the public Internet. Clients that begin the TLS handshake, but
       are unable to agree on a common cipher, may not be  able  to  send  any
       email  to  the  SMTP server. Using a restricted cipher list may be more
       appropriate for a dedicated MSA or an internal mailhub, where  one  can
       exert some control over the TLS software and settings of the connecting
       clients.

       Note: do not use "" quotes around the parameter value.

       This feature is available with Postfix version 2.2. It is not used with
       Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       opportunistic TLS encryption.  Cipher  types  listed  in  smtpd_tls_ex-
       clude_ciphers are excluded from the base definition of the selected ci-
       pher grade.  The default value is "medium" for Postfix  releases  after
       the middle of 2015, "export" for older releases.

       When   TLS   is   mandatory   the   cipher  grade  is  chosen  via  the
       smtpd_tls_mandatory_ciphers configuration parameter, see there for syn-
       tax details.

       This  feature is available in Postfix 2.6 and later. With earlier Post-
       fix releases only the smtpd_tls_mandatory_ciphers parameter  is  imple-
       mented, and opportunistic TLS always uses "export" or better (i.e. all)
       ciphers.

smtpd_tls_dcert_file (default: empty)
       File with the Postfix SMTP server DSA certificate in PEM format.   This
       file may also contain the Postfix SMTP server private DSA key.  The DSA
       algorithm is obsolete and should not be used.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server  should  use  with
       non-export EDH ciphers.

       Instead  of  using  the  exact  same parameter sets as distributed with
       other TLS packages, it is more secure to generate your own set  of  pa-
       rameters with something like the following commands:

           openssl dhparam -out /etc/postfix/dh512.pem 512
           openssl dhparam -out /etc/postfix/dh1024.pem 1024
           openssl dhparam -out /etc/postfix/dh2048.pem 2048

       It is safe to share the same DH parameters between multiple Postfix in-
       stances.  If you prefer, you can generate separate parameters for  each
       instance.

       If you want to take maximal advantage of ciphers that offer forward se-
       crecy see the Getting started section of  FORWARD_SECRECY_README.   The
       full document conveniently presents all information about Postfix "per-
       fect" forward secrecy support in one place: what  forward  secrecy  is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server  should  use  with
       export-grade  EDH  ciphers.   The  default  SMTP server cipher grade is
       "medium" with Postfix releases after the middle of 2015, and as  a  re-
       sult export-grade cipher suites are by default not used.

       See  also the discussion under the smtpd_tls_dh1024_param_file configu-
       ration parameter.

       Example:

       smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
       File with the Postfix SMTP server DSA private key in PEM format.   This
       file  may be combined with the Postfix SMTP server DSA certificate file
       specified with $smtpd_tls_dcert_file. The DSA algorithm is obsolete and
       should not be used.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)
       File  with  the  Postfix  SMTP  server ECDSA certificate in PEM format.
       This file may also contain the Postfix SMTP server private  ECDSA  key.
       With Postfix >= 3.4 the preferred way to configure server keys and cer-
       tificates is via the "smtpd_tls_chain_files" parameter.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
       File  with  the  Postfix  SMTP  server ECDSA private key in PEM format.
       This file may be combined with the Postfix SMTP server  ECDSA  certifi-
       cate  file  specified with $smtpd_tls_eccert_file.  With Postfix >= 3.4
       the preferred way to configure server keys and certificates is via  the
       "smtpd_tls_chain_files" parameter.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)
       The Postfix SMTP server security  grade  for  ephemeral  elliptic-curve
       Diffie-Hellman (EECDH) key exchange.

       The available choices are:

       none   Don't  use  EECDH.  Ciphers  based on EECDH key exchange will be
              disabled. This is the default in Postfix versions 2.6 and 2.7.

       strong Use EECDH with approximately 128 bits of security at  a  reason-
              able  computational  cost.  This  is  the  current best-practice
              trade-off between security and computational efficiency. This is
              the default in Postfix version 2.8 and later.

       ultra  Use  EECDH  with  approximately 192 bits of security at computa-
              tional cost that is approximately  twice  as  high  as  128  bit
              strength  ECC. Barring significant progress in attacks on ellip-
              tic curve crypto-systems, the "strong" curve is  sufficient  for
              most users.

       auto   Use  the  most  preferred  curve  that  is supported by both the
              client and the server.  This setting  requires  Postfix  >=  3.2
              compiled  and linked with OpenSSL >= 1.0.2.  This is the default
              setting under the above conditions.

       If you want to take maximal advantage of ciphers that offer forward se-
       crecy  see  the Getting started section of FORWARD_SECRECY_README.  The
       full document conveniently presents all information about Postfix "per-
       fect"  forward  secrecy  support in one place: what forward secrecy is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later on platforms where EC algorithms
       have not been disabled by the vendor.

smtpd_tls_exclude_ciphers (default: empty)
       List  of ciphers or cipher types to exclude from the SMTP server cipher
       list at all TLS security levels. Excluding valid ciphers can create in-
       teroperability  problems. DO NOT exclude ciphers unless it is essential
       to do so. This is not an OpenSSL cipherlist; it is a simple list  sepa-
       rated by whitespace and/or commas. The elements are a single cipher, or
       one or more "+" separated cipher properties, in which case only ciphers
       matching all the properties are excluded.

       Examples (some of these will cause problems):

           smtpd_tls_exclude_ciphers = aNULL
           smtpd_tls_exclude_ciphers = MD5, DES
           smtpd_tls_exclude_ciphers = DES+MD5
           smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtpd_tls_exclude_ciphers = kEDH+aRSA

       The first setting disables anonymous ciphers. The next setting disables
       ciphers that use the MD5 digest algorithm or the (single)  DES  encryp-
       tion  algorithm. The next setting disables ciphers that use MD5 and DES
       together.  The next setting disables the two ciphers  "AES256-SHA"  and
       "DES-CBC3-MD5".  The  last  setting disables ciphers that use "EDH" key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)
       The message digest algorithm to construct remote  SMTP  client-certifi-
       cate  fingerprints  or  public key fingerprints (Postfix 2.9 and later)
       for check_ccert_access and permit_tls_clientcerts.  The  default  algo-
       rithm  is  md5, for backwards compatibility with Postfix releases prior
       to 2.5.

       Advances in hash function cryptanalysis have led to  md5  being  depre-
       cated in favor of sha1.  However, as long as there are no known "second
       pre-image" attacks against md5, its use in this context  can  still  be
       considered safe.

       While  additional  digest algorithms are often available with OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For  ex-
       ample:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To  extract  the  public key fingerprint from an X.509 certificate, you
       need to extract the public key from the certificate and compute the ap-
       propriate  digest  of its DER (ASN.1) encoding. With OpenSSL the "-pub-
       key" option of the "x509" command extracts the  public  key  always  in
       "PEM"  format.  We pipe the result to another OpenSSL command that con-
       verts the key to DER and then to the "dgst" command to compute the fin-
       gerprint.

       The  actual  command  to transform the key to DER format depends on the
       version of OpenSSL used. With OpenSSL 1.0.0 and later, the "pkey"  com-
       mand  supports  all  key types. With OpenSSL 0.9.8 and earlier, the key
       type is always RSA (nobody uses DSA, and EC keys  are  not  fully  sup-
       ported by 0.9.8), so the "rsa" command is used.

           # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl pkey -pubin -outform DER |
               openssl dgst -sha1 -c
           (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

           # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl rsa -pubin -outform DER |
               openssl dgst -md5 -c
           (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fin-
       gerprint and public key fingerprint when  the  TLS  loglevel  is  2  or
       higher.

       Note:  Postfix  2.9.0-2.9.5  computed the public key fingerprint incor-
       rectly. To use public-key fingerprints, upgrade  to  Postfix  2.9.6  or
       later.

       Example: client-certificate access table, with sha1 fingerprints:

           /etc/postfix/main.cf:
               smtpd_tls_fingerprint_digest = sha1
               smtpd_client_restrictions =
                   check_ccert_access hash:/etc/postfix/access,
                   reject
           /etc/postfix/access:
               # Action folded to next line...
               AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
                   OK
               85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
                   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
       File  with the Postfix SMTP server RSA private key in PEM format.  This
       file may be combined with the Postfix SMTP server RSA certificate  file
       specified with $smtpd_tls_cert_file.  With Postfix >= 3.4 the preferred
       way  to  configure  server   keys   and   certificates   is   via   the
       "smtpd_tls_chain_files" parameter.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

smtpd_tls_loglevel (default: 0)
       Enable  additional  Postfix  SMTP server logging of TLS activity.  Each
       logging level also includes the information that is logged at  a  lower
       logging level.

              0 Disable logging of TLS activity.

              1  Log  only  a summary message on TLS handshake completion - no
              logging of client certificate trust-chain verification errors if
              client  certificate  verification is not required.  With Postfix
              2.8 and earlier, log the summary message, peer certificate  sum-
              mary  information  and unconditionally log trust-chain verifica-
              tion errors.

              2 Also log levels during TLS negotiation.

              3 Also  log  hexadecimal  and  ASCII  dump  of  TLS  negotiation
              process.

              4  Also  log hexadecimal and ASCII dump of complete transmission
              after STARTTLS.

       Do not use "smtpd_tls_loglevel = 2" or higher except in case  of  prob-
       lems. Use of loglevel 4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       mandatory TLS encryption. The default grade ("medium") is  sufficiently
       strong  that  any  benefit  from globally restricting TLS sessions to a
       more stringent grade is likely negligible, especially  given  the  fact
       that  many  implementations  still  do  not  offer any stronger ("high"
       grade) ciphers, while those that do, will always use "high"  grade  ci-
       phers.  So  insisting on "high" grade ciphers is generally counter-pro-
       ductive. Allowing "export" or "low" ciphers is  typically  not  a  good
       idea,  as  systems  limited  to  just  these  are  limited  to obsolete
       browsers. No known SMTP clients fail to support at least  one  "medium"
       or "high" grade cipher.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or stronger OpenSSL ciphers.  The underly-
              ing cipherlist is specified via the  tls_export_cipherlist  con-
              figuration  parameter,  which you are strongly encouraged to not
              change.  This choice is insecure and SHOULD NOT be used.

       low    Enable "LOW" grade or stronger OpenSSL ciphers.  The  underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter, which you are  strongly  encouraged  to  not  change.
              This choice is insecure and SHOULD NOT be used.

       medium Enable  "MEDIUM"  grade  or  stronger OpenSSL ciphers. These use
              128-bit or longer symmetric bulk-encryption keys.  This  is  the
              default  minimum  strength for mandatory TLS encryption. The un-
              derlying cipherlist is specified via  the  tls_medium_cipherlist
              configuration  parameter,  which  you are strongly encouraged to
              not change.

       high   Enable only "HIGH" grade OpenSSL  ciphers.  The  underlying  ci-
              pherlist  is specified via the tls_high_cipherlist configuration
              parameter, which you are strongly encouraged to not change.

       null   Enable only the "NULL" OpenSSL ciphers, these provide  authenti-
              cation  without encryption.  This setting is only appropriate in
              the rare case that all clients are prepared to use NULL  ciphers
              (not normally enabled in TLS clients). The underlying cipherlist
              is specified via the tls_null_cipherlist  configuration  parame-
              ter, which you are strongly encouraged to not change.

       Cipher   types   listed   in   smtpd_tls_mandatory_exclude_ciphers   or
       smtpd_tls_exclude_ciphers are excluded from the base definition of  the
       selected  cipher  grade. See smtpd_tls_ciphers for cipher controls that
       apply to opportunistic TLS.

       The underlying cipherlists for grades other than "null" include  anony-
       mous ciphers, but these are automatically filtered out if the server is
       configured to ask for remote SMTP client certificates.   You  are  very
       unlikely  to  need to take any steps to exclude anonymous ciphers, they
       are excluded automatically as required.  If you must exclude  anonymous
       ciphers  even  when Postfix does not need or use peer certificates, set
       "smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers  only
       when  TLS  is  enforced, set "smtpd_tls_mandatory_exclude_ciphers = aN-
       ULL".

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to exclude from the  Postfix
       SMTP  server  cipher  list at mandatory TLS security levels.  This list
       works in addition to the exclusions listed  with  smtpd_tls_exclude_ci-
       phers (see there for syntax details).

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: !SSLv2, !SSLv3)
       The  SSL/TLS  protocols accepted by the Postfix SMTP server with manda-
       tory TLS encryption. If the list is  empty,  the  server  supports  all
       available  SSL/TLS  protocol  versions.  A non-empty value is a list of
       protocol names separated by whitespace, commas  or  colons.   The  sup-
       ported  protocol  names  are  "SSLv2", "SSLv3" and "TLSv1", and are not
       case sensitive. The default value is "!SSLv2, !SSLv3" for  Postfix  re-
       leases after the middle of 2015, "!SSLv2" for older releases.

       With Postfix >= 2.5 the parameter syntax was expanded to support proto-
       col  exclusions.  One  can  explicitly  exclude  "SSLv2"   by   setting
       "smtpd_tls_mandatory_protocols  =  !SSLv2". To exclude both "SSLv2" and
       "SSLv3" set "smtpd_tls_mandatory_protocols = !SSLv2,  !SSLv3".  Listing
       the  protocols  to  include,  rather than protocols to exclude, is sup-
       ported, but not recommended. The exclusion form  more  closely  matches
       the underlying OpenSSL interface semantics.

       Note:  As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". When Postfix <= 2.5  is  linked  against  OpenSSL  1.0.1  or
       later,  these,  or any other new protocol versions, cannot be disabled.
       The latest patch levels of Postfix >= 2.6, and all versions of  Postfix
       >= 2.10 can disable support for "TLSv1.1" or "TLSv1.2".

       OpenSSL  1.1.1  introduces  support for "TLSv1.3".  With Postfix >= 3.4
       (or patch releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2) this can be dis-
       abled, if need be, via "!TLSv1.3".

       Example:

       # Preferred syntax with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Legacy syntax:
       smtpd_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: !SSLv2, !SSLv3)
       List  of TLS protocols that the Postfix SMTP server will exclude or in-
       clude with opportunistic TLS encryption. The default value is  "!SSLv2,
       !SSLv3"  for Postfix releases after the middle of 2015, empty for older
       releases allowing all protocols to be used with opportunistic  TLS.   A
       non-empty  value  is  a list of protocol names separated by whitespace,
       commas or colons.  The supported protocol names  are  "SSLv2",  "SSLv3"
       and "TLSv1", and are not case sensitive.

       Note:  As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". The latest patch levels of Postfix >= 2.6, and all  versions
       of Postfix >= 2.10 can disable support for "TLSv1.1" or "TLSv1.2".

       OpenSSL  1.1.1  introduces  support for "TLSv1.3".  With Postfix >= 3.4
       (or patch releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2) this can be dis-
       abled, if need be, via "!TLSv1.3".

       To  include  a  protocol  list its name, to exclude it, prefix the name
       with a "!" character.  To  exclude  SSLv2  for  opportunistic  TLS  set
       "smtpd_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtpd_tls_protocols = !SSLv2, !SSLv3". Explicitly listing  the  proto-
       cols  to  include,  rather than protocols to exclude, is supported, but
       not recommended.  The exclusion form more closely matches the  underly-
       ing OpenSSL interface semantics.

       Example:
       smtpd_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)
       Request  that the Postfix SMTP server produces Received:  message head-
       ers that include information about the protocol  and  cipher  used,  as
       well as the remote SMTP client CommonName and client certificate issuer
       CommonName.  This is disabled by default, as  the  information  may  be
       modified  in transit through other mail servers.  Only information that
       was recorded by the final destination can be trusted.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
       With mandatory TLS encryption, require a  trusted  remote  SMTP  client
       certificate  in order to allow TLS connections to proceed.  This option
       implies "smtpd_tls_ask_ccert = yes".

       When TLS encryption is optional, this setting is ignored with a warning
       written to the mail log.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)
       The  SMTP  TLS  security  level  for  the  Postfix  SMTP server; when a
       non-empty value is specified, this overrides  the  obsolete  parameters
       smtpd_use_tls  and  smtpd_enforce_tls.  This  parameter is ignored with
       "smtpd_tls_wrappermode = yes".

       Specify one of the following security levels:

       none   TLS will not be used.

       may    Opportunistic TLS: announce  STARTTLS  support  to  remote  SMTP
              clients, but do not require that clients use TLS encryption.

       encrypt
              Mandatory  TLS  encryption:  announce STARTTLS support to remote
              SMTP clients, and require that clients use TLS  encryption.  Ac-
              cording  to  RFC 2487 this MUST NOT be applied in case of a pub-
              licly-referenced SMTP server. Instead,  this  option  should  be
              used only on dedicated servers.

       Note  1:  the  "fingerprint", "verify" and "secure" levels are not sup-
       ported here.  The Postfix SMTP server logs a warning and uses "encrypt"
       instead.  To verify remote SMTP client certificates, see TLS_README for
       a discussion of the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and  per-
       mit_tls_clientcerts features.

       Note  2: The parameter setting "smtpd_tls_security_level = encrypt" im-
       plies "smtpd_tls_auth_only = yes".

       Note 3: when invoked via  "sendmail  -bs",  Postfix  will  never  offer
       STARTTLS  due  to  insufficient privileges to access the server private
       key. This is intended behavior.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
       Name of the file containing the optional Postfix SMTP server  TLS  ses-
       sion  cache. Specify a database type that supports enumeration, such as
       btree or sdbm; there is no need to support concurrent access.  The file
       is  created if it does not exist. The smtpd(8) daemon does not use this
       parameter directly, rather the cache is implemented indirectly  in  the
       tlsmgr(8)  daemon.  This  means that per-smtpd-instance master.cf over-
       rides of this parameter are not effective. Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
       base, $smtp_tls_session_cache_database (and with Postfix 2.3 and  later
       $lmtp_tls_session_cache_database), needs to be stored separately. It is
       not at this time possible to store multiple caches in  a  single  data-
       base.

       Note:  dbm  databases  are  not  suitable.  TLS session objects are too
       large.

       As of version 2.5, Postfix no longer uses root privileges when  opening
       this  file.  The  file  should  now  be  stored under the Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix  directory  is  redirected to the Postfix-owned data_direc-
       tory, and a warning is logged.

       As of Postfix 2.11 the preferred mechanism for  session  resumption  is
       RFC  5077 TLS session tickets, which don't require server-side storage.
       Consequently, for Postfix >= 2.11 this parameter  should  generally  be
       left  empty.   TLS session tickets require an OpenSSL library (at least
       version 0.9.8h) that provides full support for this TLS extension.  See
       also smtpd_tls_session_cache_timeout.

       Example:

       smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache

       This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
       The  expiration  time of Postfix SMTP server TLS session cache informa-
       tion. A cache cleanup is performed periodically  every  $smtpd_tls_ses-
       sion_cache_timeout  seconds. As with $smtpd_tls_session_cache_database,
       this parameter is implemented in the  tlsmgr(8)  daemon  and  therefore
       per-smtpd-instance master.cf overrides are not possible.

       As  of  Postfix 2.11 this setting cannot exceed 100 days.  If set <= 0,
       session caching is disabled, not just via the database,  but  also  via
       RFC  5077 TLS session tickets, which don't require server-side storage.
       If set to a positive value less than 2 minutes, the minimum value of  2
       minutes  is  used  instead.  TLS session tickets require an OpenSSL li-
       brary (at least version 0.9.8h) that provides full support for this TLS
       extension.

       This feature is available in Postfix 2.2 and later, and updated for TLS
       session ticket support in Postfix 2.11.

smtpd_tls_wrappermode (default: no)
       Run the Postfix SMTP server in the non-standard "wrapper" mode, instead
       of using the STARTTLS command.

       If  you  want  to  support  this service, enable a special port in mas-
       ter.cf, and specify "-o smtpd_tls_wrappermode=yes" on the SMTP server's
       command line. Port 465 (smtps) was once chosen for this purpose.

       This feature is available in Postfix 2.2 and later.

smtpd_upstream_proxy_protocol (default: empty)
       The  name  of the proxy protocol used by an optional before-smtpd proxy
       agent. When a proxy agent is used, this protocol conveys local and  re-
       mote  address and port information.  Specify "smtpd_upstream_proxy_pro-
       tocol = haproxy" to enable the haproxy protocol.

       NOTE: To use the nginx proxy with smtpd(8), enable the XCLIENT protocol
       with  smtpd_authorized_xclient_hosts. This supports SASL authentication
       in the proxy agent (Postfix 2.9 and later).

       This feature is available in Postfix 2.10 and later.

smtpd_upstream_proxy_timeout (default: 5s)
       The time limit for the proxy  protocol  specified  with  the  smtpd_up-
       stream_proxy_protocol parameter.

       This feature is available in Postfix 2.10 and later.

smtpd_use_tls (default: no)
       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients,
       but do not require that clients use TLS encryption.

       Note: when invoked via "sendmail -bs", Postfix will never offer  START-
       TLS  due  to  insufficient privileges to access the server private key.
       This is intended behavior.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtpd_tls_security_level instead.

smtputf8_autodetect_classes (default: sendmail, verify)
       Detect  that a message requires SMTPUTF8 support for the specified mail
       origin classes.  This is a workaround to avoid chicken-and-egg problems
       during  the initial SMTPUTF8 roll-out in environments with pre-existing
       mail flows that contain UTF8. Those mail flows should not break because
       Postfix  suddenly refuses to deliver such mail to down-stream MTAs that
       don't announce SMTPUTF8 support.

       The problem is that Postfix cannot rely solely on the sender's declara-
       tion  that a message requires SMTPUTF8 support, because UTF8 may be in-
       troduced during local processing (for example, the client  hostname  in
       Postfix's  Received:  header, adding @$myorigin or .$mydomain to an in-
       complete address, address rewriting, alias expansion, automatic BCC re-
       cipients, local forwarding, and changes made by header checks or Milter
       applications).

       For now, the default is to  enable  "SMTPUTF8  required"  autodetection
       only  for Postfix sendmail command-line submissions and address verifi-
       cation probes.  This may change once SMTPUTF8  support  achieves  world
       domination.   However, sites that add UTF8 content via local processing
       (see above) should autodetect the need for  SMTPUTF8  support  for  all
       email.

       Specify one or more of the following:

        sendmail
              Submission with the Postfix sendmail(1) command.

        smtpd Mail received with the smtpd(8) daemon.

        qmqpd Mail received with the qmqpd(8) daemon.

        forward
              Local  forwarding  or aliasing.  When a message is received with
              "SMTPUTF8 required", then the forwarded (aliased) message always
              has "SMTPUTF8 required".

        bounce
              Submission  by the bounce(8) daemon.  When a message is received
              with "SMTPUTF8 required", then the delivery status  notification
              always has "SMTPUTF8 required".

        notify
              Postmaster notification from the smtp(8) or smtpd(8) daemon.

        verify
              Address verification probe from the verify(8) daemon.

        all   Enable SMTPUTF8 autodetection for all mail.

       This feature is available in Postfix 3.0 and later.

smtputf8_enable (default: yes)
       Enable  preliminary SMTPUTF8 support for the protocols described in RFC
       6531..6533. This requires that Postfix is built to support these proto-
       cols.

       This feature is available in Postfix 3.0 and later.

soft_bounce (default: no)
       Safety  net to keep mail queued that would otherwise be returned to the
       sender.  This parameter disables locally-generated bounces, changes the
       handling  of negative responses from remote servers, content filters or
       plugins, and prevents the Postfix SMTP server from rejecting mail  per-
       manently by changing 5xx reply codes into 4xx.  However, soft_bounce is
       no cure for address rewriting mistakes or mail routing mistakes.

       Note: "soft_bounce = yes" is in some  cases  implemented  by  modifying
       server  responses. Therefore, the response that Postfix logs may differ
       from the response that Postfix actually sends or receives.

       Example:

       soft_bounce = yes

stale_lock_time (default: 500s)
       The time after which a stale exclusive  mailbox  lockfile  is  removed.
       This is used for delivery to file or mailbox.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

stress (default: empty)
       This feature is documented in the STRESS_README document.

       This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)
       Reject mail with 8-bit text in message headers. This blocks  mail  from
       poorly written applications.

       This  feature  should  not be enabled on a general purpose mail server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
       Enable both strict_7bit_headers and strict_8bitmime_body.

       This feature should not be enabled on a general  purpose  mail  server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
       Reject  8-bit message body text without 8-bit MIME content encoding in-
       formation.  This blocks mail from poorly written applications.

       Unfortunately, this also rejects majordomo approval requests  when  the
       included request contains valid 8-bit MIME mail, and it rejects bounces
       from mailers that do not MIME encapsulate 8-bit content  (for  example,
       bounces from qmail or from old versions of Postfix).

       This  feature  should  not be enabled on a general purpose mail server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)
       Defer delivery when a mailbox file is not owned by its recipient.   The
       default setting is not backwards compatible.

       This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)
       Reject mail with invalid Content-Transfer-Encoding: information for the
       message/* or multipart/* MIME content types.   This  blocks  mail  from
       poorly written software.

       This  feature  should  not be enabled on a general purpose mail server,
       because it will reject mail after a single violation.

       This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
       Require that addresses received in SMTP MAIL FROM and RCPT TO  commands
       are  enclosed  with <>, and that those addresses do not contain RFC 822
       style comments or phrases.  This stops mail from poorly  written  soft-
       ware.

       By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM
       and RCPT TO addresses.

strict_smtputf8 (default: no)
       Enable stricter enforcement of the SMTPUTF8 protocol. The Postfix  SMTP
       server  accepts UTF8 sender or recipient addresses only when the client
       requests an SMTPUTF8 mail transaction.

       This feature is available in Postfix 3.0 and later.

sun_mailtool_compatibility (default: no)
       Obsolete SUN mailtool compatibility feature. Instead, use  "mailbox_de-
       livery_lock = dotlock".

swap_bangpath (default: yes)
       Enable  the  rewriting of "site!user" into "user@site".  This is neces-
       sary if your machine is connected to UUCP networks.  It is  enabled  by
       default.

       Note:  with  Postfix version 2.2, message header address rewriting hap-
       pens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches  $lo-
              cal_header_rewrite_clients,

       o      The   message   is  received  from  the  network,  and  the  re-
              mote_header_rewrite_domain  parameter  specifies   a   non-empty
              value.

       To   get   the  behavior  before  Postfix  version  2.2,  specify  "lo-
       cal_header_rewrite_clients = static:all".

       Example:

       swap_bangpath = no

syslog_facility (default: mail)
       The syslog facility of Postfix logging. Specify a facility  as  defined
       in syslog.conf(5). The default facility is "mail".

       Warning:  a non-default syslog_facility setting takes effect only after
       a Postfix process has completed initialization.  Errors during  process
       initialization  will be logged with the default facility.  Examples are
       errors while parsing the command line arguments, and errors  while  ac-
       cessing the Postfix main.cf configuration file.

syslog_name (default: see postconf -d output)
       A  prefix  that  is prepended to the process name in syslog records, so
       that, for example, "smtpd" becomes "prefix/smtpd".

       Warning: a non-default syslog_name setting takes effect  only  after  a
       Postfix  process  has  completed  initialization. Errors during process
       initialization will be logged with the default name. Examples  are  er-
       rors while parsing the command line arguments, and errors while access-
       ing the Postfix main.cf configuration file.

tcp_windowsize (default: 0)
       An optional workaround for  routers  that  break  TCP  window  scaling.
       Specify  a  value > 0 and < 65536 to enable this feature.  With Postfix
       TCP servers (smtpd(8), qmqpd(8)), this feature is  implemented  by  the
       Postfix master(8) daemon.

       To  change  this  parameter without stopping Postfix, you need to first
       terminate all Postfix TCP servers:

           # postconf -e master_service_disable=inet
           # postfix reload

       This immediately terminates all processes that accept  network  connec-
       tions.   Next, you enable Postfix TCP servers with the updated tcp_win-
       dowsize setting:

           # postconf -e tcp_windowsize=65535 master_service_disable=
           # postfix reload

       If you skip these  steps  with  a  running  Postfix  system,  then  the
       tcp_windowsize  change will work only for Postfix TCP clients (smtp(8),
       lmtp(8)).

       This feature is available in Postfix 2.6 and later.

tls_append_default_CA (default: no)
       Append the system-supplied default Certification Authority certificates
       to  the  ones specified with *_tls_CApath or *_tls_CAfile.  The default
       is "no"; this prevents Postfix from trusting  third-party  certificates
       and giving them relay permission with permit_tls_all_clientcerts.

       This  feature  is available in Postfix 2.4.15, 2.5.11, 2.6.8, 2.7.2 and
       later versions. Specify "tls_append_default_CA  =  yes"  for  backwards
       compatibility,  to  avoid  breaking certificate verification with sites
       that don't use permit_tls_all_clientcerts.

tls_daemon_random_bytes (default: 32)
       The number of pseudo-random bytes that an smtp(8) or  smtpd(8)  process
       requests from the tlsmgr(8) server in order to seed its internal pseudo
       random number generator (PRNG).  The default of 32 bytes (equivalent to
       256 bits) is sufficient to generate a 128bit (or 168bit) session key.

       This feature is available in Postfix 2.2 and later.

tls_dane_digest_agility (default: on)
       Configure  RFC7671  DANE  TLSA digest algorithm agility.  Do not change
       this setting from its default value.

       See Section 8 of RFC7671 for correct key rotation procedures.

       This feature is available in Postfix 2.11 through 3.1.  Postfix 3.2 and
       later  ignore this configuration parameter and behave as though it were
       set to "on".

tls_dane_digests (default: sha512 sha256)
       DANE TLSA (RFC 6698, RFC  7671,  RFC  7672)  resource-record  "matching
       type" digest algorithms in descending preference order.  All the speci-
       fied algorithms must be supported by the  underlying  OpenSSL  library,
       otherwise the Postfix SMTP client will not support DANE TLSA security.

       Specify  a  list of digest names separated by commas and/or whitespace.
       Each digest name may be followed by  an  optional  "=<number>"  suffix.
       For  example,  "sha512"  may  instead  be  specified  as "sha512=2" and
       "sha256" may instead be specified as "sha256=1".  The  optional  number
       must  match  the <a href="https://www.iana.org/assignments/dane-parame-
       ters/dane-parameters.xhtml#matching-types" >IANA assigned TLSA matching
       type  number  the  algorithm in question.  Postfix will check this con-
       straint for the algorithms it knows about.   Additional  matching  type
       algorithms registered with IANA can be added with explicit numbers pro-
       vided they are supported by OpenSSL.

       Invalid list elements are logged with a warning and disable  DANE  sup-
       port.   TLSA  RRs that specify digests not included in the list are ig-
       nored with a warning.

       Note: It is unwise to omit sha256 from the digest  list.   This  digest
       algorithm  is  the  only mandatory to implement digest algorithm in RFC
       6698, and many servers are expected  publish  TLSA  records  with  just
       sha256  digests.   Unless one of the standard digests is seriously com-
       promised and servers have had ample time to update their  TLSA  records
       you  should  not  omit any standard digests, just arrange them in order
       from strongest to weakest.

       This feature is available in Postfix 2.11 and later.

tls_dane_trust_anchor_digest_enable (default: yes)
       Enable support for RFC 6698 (DANE TLSA) DNS records  that  contain  di-
       gests  of trust-anchors with certificate usage "2".  Do not change this
       setting from its default value.

       This feature is available in Postfix 2.11 through  3.1.   It  has  been
       withdrawn  in  Postfix 3.2, as trust-anchor TLSA records are now widely
       used and have proved sufficiently reliable.  Postfix 3.2 and later  ig-
       nore  this configuration parameter and behaves as though it were set to
       "yes".

tls_disable_workarounds (default: see postconf -d output)
       List or bit-mask of OpenSSL bug work-arounds to disable.

       The OpenSSL toolkit includes a set of work-arounds  for  buggy  SSL/TLS
       implementations.  Applications,  such as Postfix, that want to maximize
       interoperability ask the OpenSSL library to enable the full set of rec-
       ommended work-arounds.

       From  time to time, it is discovered that a work-around creates a secu-
       rity issue, and should no longer be used. If  upgrading  OpenSSL  to  a
       fixed  version  is  not  an  option or an upgrade is not available in a
       timely manner, or in closed environments  where  no  buggy  clients  or
       servers  exist,  it  may  be  appropriate to disable some or all of the
       OpenSSL interoperability work-arounds. This parameter  specifies  which
       bug work-arounds to disable.

       If  the  value  of the parameter is a hexadecimal long integer starting
       with "0x", the bug work-arounds corresponding to the bits specified  in
       its  value  are  removed  from the SSL_OP_ALL work-around bit-mask (see
       openssl/ssl.h and SSL_CTX_set_options(3)). You can  specify  more  bits
       than  are  present  in  SSL_OP_ALL, excess bits are ignored. Specifying
       0xFFFFFFFF disables all bug-workarounds on a 32-bit system. This should
       also  be  sufficient  on 64-bit systems, until OpenSSL abandons support
       for 32-bit systems and starts using  the  high  32  bits  of  a  64-bit
       bug-workaround mask.

       Otherwise,  the  parameter  is a white-space or comma separated list of
       specific named bug work-arounds chosen from the list below. It is  pos-
       sible that your OpenSSL version includes new bug work-arounds added af-
       ter your Postfix source code was last updated, in  that  case  you  can
       only disable one of these via the hexadecimal syntax above.

       CRYPTOPRO_TLSEXT_BUG
              New with GOST support in OpenSSL 1.0.0.

       DONT_INSERT_EMPTY_FRAGMENTS
              See SSL_CTX_set_options(3)

       LEGACY_SERVER_CONNECT
              See SSL_CTX_set_options(3)

       MICROSOFT_BIG_SSLV3_BUFFER
              See SSL_CTX_set_options(3)

       MICROSOFT_SESS_ID_BUG
              See SSL_CTX_set_options(3)

       MSIE_SSLV2_RSA_PADDING
              also   aliased  as  CVE-2005-2969.  Postfix  2.8  disables  this
              work-around by default with OpenSSL versions  that  may  predate
              the fix. Fixed in OpenSSL 0.9.7h and OpenSSL 0.9.8a.

       NETSCAPE_CHALLENGE_BUG
              See SSL_CTX_set_options(3)

       NETSCAPE_REUSE_CIPHER_CHANGE_BUG
              also   aliased  as  CVE-2010-4180.  Postfix  2.8  disables  this
              work-around by default with OpenSSL versions  that  may  predate
              the fix. Fixed in OpenSSL 0.9.8q and OpenSSL 1.0.0c.

       SSLEAY_080_CLIENT_DH_BUG
              See SSL_CTX_set_options(3)

       SSLREF2_REUSE_CERT_TYPE_BUG
              See SSL_CTX_set_options(3)

       TLS_BLOCK_PADDING_BUG
              See SSL_CTX_set_options(3)

       TLS_D5_BUG
              See SSL_CTX_set_options(3)

       TLS_ROLLBACK_BUG
              See  SSL_CTX_set_options(3).   This is disabled in OpenSSL 0.9.7
              and later. Nobody should still be using 0.9.6!

       TLSEXT_PADDING
              Postfix >= 3.4. See SSL_CTX_set_options(3).

       This feature is available in Postfix 2.8 and later.

tls_eecdh_auto_curves (default: see postconf -d output)
       The prioritized list of elliptic curves supported by the  Postfix  SMTP
       client  and  server.   These curves are used by the Postfix SMTP server
       when "smtpd_tls_eecdh_grade = auto".  The selected curves must  be  im-
       plemented  by  OpenSSL  and be standardized for use in TLS (RFC 4492 or
       its imminent successor).  It is unwise  to  list  only  "bleeding-edge"
       curves  supported  by  a  small subset of clients.  The default list is
       suitable for most users.

       Postfix skips curve names that are unknown  to  OpenSSL,  or  that  are
       known  but not yet implemented.  This makes it possible to "anticipate"
       support for curves that should be used once they become available.   In
       particular,  in some OpenSSL versions, the new RFC 8031 curves "X25519"
       and "X448" may be known by name, but ECDH support for  either  or  both
       may  be  missing.  These curves may appear in the default value of this
       parameter, even though they'll only be usable with  later  versions  of
       OpenSSL.

       This feature is available in Postfix 3.2 and later, when it is compiled
       and linked with OpenSSL 1.0.2 or later on platforms where EC algorithms
       have not been disabled by the vendor.

tls_eecdh_strong_curve (default: prime256v1)
       The  elliptic curve used by the Postfix SMTP server for sensibly strong
       ephemeral ECDH key exchange. This curve is used  by  the  Postfix  SMTP
       server  when  "smtpd_tls_eecdh_grade  =  strong".  The phrase "sensibly
       strong" means approximately 128-bit security based on  best  known  at-
       tacks.  The  selected curve must be implemented by OpenSSL (as reported
       by ecparam(1) with the "-list_curves" option) and be one of the  curves
       listed  in  Section  5.1.1 of RFC 4492. You should not generally change
       this setting.  Remote SMTP client  implementations  must  support  this
       curve  for EECDH key exchange to take place.  It is unwise to choose an
       "bleeding-edge" curve supported by only a small subset of clients.

       The default "strong" curve is rated in  NSA  Suite  B  for  information
       classified up to SECRET.

       Note: elliptic curve names are poorly standardized; different standards
       groups are assigning different names to  the  same  underlying  curves.
       The curve with the X9.62 name "prime256v1" is also known under the SECG
       name "secp256r1", but OpenSSL does not recognize the latter name.

       If you want to take maximal advantage of ciphers that offer forward se-
       crecy  see  the Getting started section of FORWARD_SECRECY_README.  The
       full document conveniently presents all information about Postfix "per-
       fect"  forward  secrecy  support in one place: what forward secrecy is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later on platforms where EC algorithms
       have not been disabled by the vendor.

tls_eecdh_ultra_curve (default: secp384r1)
       The elliptic curve used by the Postfix SMTP server for maximally strong
       ephemeral ECDH key exchange. This curve is used  by  the  Postfix  SMTP
       server  when  "smtpd_tls_eecdh_grade  =  ultra".  The phrase "maximally
       strong" means approximately 192-bit security based on  best  known  at-
       tacks.   This  additional strength comes at a significant computational
       cost, most users should instead set "smtpd_tls_eecdh_grade  =  strong".
       The  selected  curve must be implemented by OpenSSL (as reported by ec-
       param(1) with the "-list_curves" option)  and  be  one  of  the  curves
       listed  in  Section  5.1.1 of RFC 4492. You should not generally change
       this setting.

       This default "ultra" curve is rated in  NSA  Suite  B  for  information
       classified up to TOP SECRET.

       If you want to take maximal advantage of ciphers that offer forward se-
       crecy see the Getting started section of  FORWARD_SECRECY_README.   The
       full document conveniently presents all information about Postfix "per-
       fect" forward secrecy support in one place: what  forward  secrecy  is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later on platforms where EC algorithms
       have not been disabled by the vendor.

tls_export_cipherlist (default: see postconf -d output)
       The OpenSSL cipherlist for "export" or higher grade ciphers.  This  de-
       fines  the  meaning  of  the  "export"  setting  in  smtpd_tls_ciphers,
       smtpd_tls_mandatory_ciphers,  smtp_tls_ciphers,  smtp_tls_mandatory_ci-
       phers,  lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers.  With Postfix
       releases before the middle of 2015 this is the default  cipherlist  for
       the  opportunistic  ("may")  TLS client security level and also the de-
       fault cipherlist for the SMTP server. You are  strongly  encouraged  to
       not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_fast_shutdown_enable (default: yes)
       A workaround for implementations that hang Postfix while shuting down a
       TLS session, until Postfix times out. With this enabled,  Postfix  will
       not wait for the remote TLS peer to respond to a TLS later.

       This  feature  was  introduced  with  Postfix 3.4.6, 3.3.5, 3.2.10, and
       3.1.13.

tls_high_cipherlist (default: see postconf -d output)
       The OpenSSL cipherlist for "high" grade ciphers. This defines the mean-
       ing of the "high" setting in smtpd_tls_ciphers, smtpd_tls_mandatory_ci-
       phers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,  lmtp_tls_ciphers,
       and  lmtp_tls_mandatory_ciphers.  You  are  strongly  encouraged to not
       change this setting.

       This feature is available in Postfix 2.3 and later.

tls_legacy_public_key_fingerprints (default: no)
       A temporary migration aid for sites  that  use  certificate  public-key
       fingerprints  with  Postfix  2.9.0..2.9.5, which use an incorrect algo-
       rithm. This parameter has no effect on the certificate fingerprint sup-
       port that is available since Postfix 2.2.

       Specify "tls_legacy_public_key_fingerprints = yes" temporarily, pending
       a  migration  from   configuration   files   with   incorrect   Postfix
       2.9.0..2.9.5  certificate public-key finger prints, to the correct fin-
       gerprints used by Postfix 2.9.6 and later.  To compute the correct cer-
       tificate public-key fingerprints, see TLS_README.

       This feature is available in Postfix 2.9.6 and later.

tls_low_cipherlist (default: see postconf -d output)
       The  OpenSSL cipherlist for "low" or higher grade ciphers. This defines
       the meaning of the "low" setting in smtpd_tls_ciphers, smtpd_tls_manda-
       tory_ciphers,       smtp_tls_ciphers,       smtp_tls_mandatory_ciphers,
       lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers. You are strongly  en-
       couraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: see postconf -d output)
       The  OpenSSL  cipherlist for "medium" or higher grade ciphers. This de-
       fines  the  meaning  of  the  "medium"  setting  in  smtpd_tls_ciphers,
       smtpd_tls_mandatory_ciphers,  smtp_tls_ciphers,  smtp_tls_mandatory_ci-
       phers, lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers.  This  is  the
       default cipherlist for mandatory TLS encryption in the TLS client (with
       anonymous ciphers disabled when verifying server  certificates).   This
       is  the  default cipherlist for opportunistic TLS with Postfix releases
       after the middle of 2015.  You are strongly encouraged  to  not  change
       this setting.

       This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
       The  OpenSSL cipherlist for "NULL" grade ciphers that provide authenti-
       cation without encryption. This defines the meaning of the "null"  set-
       ting  in  smtpd_mandatory_tls_ciphers,  smtp_tls_mandatory_ciphers  and
       lmtp_tls_mandatory_ciphers.  You are strongly encouraged to not  change
       this setting.

       This feature is available in Postfix 2.3 and later.

tls_preempt_cipherlist (default: no)
       With  SSLv3  and later, use the Postfix SMTP server's cipher preference
       order instead of the remote client's cipher preference order.

       By default, the OpenSSL server selects the client's most preferred  ci-
       pher  that  the  server  supports. With SSLv3 and later, the server may
       choose its own most preferred cipher that is supported (offered) by the
       client.  Setting  "tls_preempt_cipherlist  = yes" enables server cipher
       preferences.

       While server cipher selection may in some cases lead to a  more  secure
       or performant cipher choice, there is some risk of interoperability is-
       sues. In the past, some SSL clients have listed lower priority  ciphers
       that  they  did not implement correctly. If the server chooses a cipher
       that the client prefers less, it may select a cipher whose  client  im-
       plementation  is  flawed.  Most notably Windows 2003 Microsoft Exchange
       servers have flawed implementations of DES-CBC3-SHA, which OpenSSL con-
       siders  stronger  than RC4-SHA.  Enabling server cipher-suite selection
       may create interoperability issues with Windows 2003 Microsoft Exchange
       clients.

       This feature is available in Postfix 2.8 and later, in combination with
       OpenSSL 0.9.7 and later.

tls_random_bytes (default: 32)
       The number of bytes that tlsmgr(8) reads from  $tls_random_source  when
       (re)seeding  the  in-memory pseudo random number generator (PRNG) pool.
       The default of 32 bytes (256 bits) is good enough for 128bit  symmetric
       keys.  If using EGD or a device file, a maximum of 255 bytes is read.

       This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)
       Name  of  the  pseudo random number generator (PRNG) state file that is
       maintained by tlsmgr(8). The file is created when it  does  not  exist,
       and its length is fixed at 1024 bytes.

       As  of version 2.5, Postfix no longer uses root privileges when opening
       this file, and the default file location was changed from  ${config_di-
       rectory}/prng_exch to ${data_directory}/prng_exch.  As a migration aid,
       an attempt to open the file under a non-Postfix directory is redirected
       to the Postfix-owned data_directory, and a warning is logged.

       This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
       The  time between attempts by tlsmgr(8) to save the state of the pseudo
       random number generator (PRNG) to the  file  specified  with  $tls_ran-
       dom_exchange_name.

       This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
       The maximal time between attempts by tlsmgr(8) to re-seed the in-memory
       pseudo random number generator (PRNG) pool from external sources.   The
       actual  time  between re-seeding attempts is calculated using the PRNG,
       and is between 0 and the time specified.

       This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
       The external entropy source for the in-memory tlsmgr(8)  pseudo  random
       number generator (PRNG) pool. Be sure to specify a non-blocking source.
       If this source is not a regular file, the entropy source type  must  be
       prepended:   egd:/path/to/egd_socket  for  a source with EGD compatible
       socket interface, or dev:/path/to/device for a device file.

       Note: on OpenBSD systems specify /dev/arandom when  /dev/urandom  gives
       timeout errors.

       This feature is available in Postfix 2.2 and later.

tls_server_sni_maps (default: empty)
       Optional lookup tables that map names received from remote SMTP clients
       via the TLS Server Name Indication (SNI) extension to  the  appropriate
       keys  and  certificate  chains.   This  parameter is implemented in the
       Postfix TLS library, and applies to both smtpd(8) and the  SMTP  server
       mode of tlsproxy(8).

       The  lookup  key  is either the verbatim SNI domain name or an ancestor
       domain prefixed with a leading dot.  For internationalized domains, the
       lookup  key  must  be in IDNA 2008 A-label form (as required in the TLS
       SNI extension).

       When this parameter is non-empty, the Postfix SMTP server  enables  SNI
       extension  processing,  and  logs  SNI values that are invalid or don't
       match an entry in the the specified tables.  When an entry does  match,
       the  SNI name is logged as part of the connection summary at log levels
       1 and higher.

       Note that the SNI lookup tables should also have entries  for  the  do-
       mains  that  correspond  to  the Postfix SMTP server's default certifi-
       cate(s). This ensures that the remote SMTP client's TLS  SNI  extension
       gets  a  positive  response  when  it specifies one of the Postfix SMTP
       server's default domains, and ensures that the Postfix SMTP server will
       not  log  an  SNI  name  mismatch  for such a domain.  The Postfix SMTP
       server's default certificates are then only used when the client  sends
       no SNI or when it sends SNI with a domain that the server knows no cer-
       tificate(s) for.

       The mapping from an SNI domain name to a certificate chain is typically
       indirect.   In  the  input  source  files for "cdb", "hash", "btree" or
       other  tables  that  are  converted  to  on-disk  indexed   files   via
       postmap(1),  the  value  specified for each key is a list of filenames.
       When postmap(1) is used with the -F option, the generated table  stores
       for  each  lookup  key  the  base64-encoded  contents of the associated
       files.  When querying tables via postmap -Fq, the table  value  is  de-
       coded from base64, yielding the original file content, plus a new line.

       With  "regexp",  "pcre", "inline", "texthash", "static" and similar ta-
       bles that are interpreted at run-time, and don't have a separate source
       format,  the  table  value is again a list files, that are read-in when
       the table is opened.

       Thus, for example:

           $ postmap -Fq "" static:/etc/postfix/chain.pem | openssl dgst -sha1
           (stdin)= da39a3ee5e6b4b0d3255bfef95601890afd80709

       produces the same output as:

           $ (cat /etc/postfix/chain.pem; echo) | openssl dgst -sha1
           (stdin)= da39a3ee5e6b4b0d3255bfef95601890afd80709

       With tables whose content is managed outside of Postfix, such as  LDAP,
       MySQL, PostgreSQL, socketmap and tcp, the value must be a concatenation
       of the desired PEM keys and certificate chains, that  is  then  further
       encoded  to yield a single-line base64 string.  Creation of such tables
       and secure storage are outside the  responsibility  of  Postfix.   With
       "socketmap" and "tcp" the data would be transmitted in the clear.  With
       LDAP and SQL, you should generally use TLS  to  protect  the  sensitive
       data in transit.

       Typically  there  is  only  private  key  and its chain of certificates
       starting with the "leaf" certificate corresponding  to  that  key,  and
       continuing  with  the  appropriate intermediate issuer CA certificates,
       with each certificate ideally followed by  its  issuer.   Servers  that
       have  keys  and certificates for more than one algorithm (e.g.  both an
       RSA key and an ECDSA key, or even RSA, ECDSA and Ed25519) can use  mul-
       tiple  chains  concatenated together, with the key always listed before
       the corresponding certificates.

       This feature is available in Postfix 3.4 and later.

tls_session_ticket_cipher (default: Postfix >=  3.0:  aes-256-cbc,  Postfix  <
       3.0: aes-128-cbc)
       Algorithm  used to encrypt RFC5077 TLS session tickets.  This algorithm
       must use CBC mode, have a 128-bit block  size,  and  must  have  a  key
       length between 128 and 256 bits.  The default is aes-256-cbc.  Overrid-
       ing the default to choose a different algorithm is discouraged.

       Setting this parameter empty disables session  ticket  support  in  the
       Postfix  SMTP server.  Another way to disable session ticket support is
       via the tls_ssl_options parameter.

       This feature is available in Postfix 3.0 and later.

tls_ssl_options (default: empty)
       List or bit-mask of OpenSSL options to enable.

       The OpenSSL toolkit provides a set of options that applications can en-
       able  to  tune the OpenSSL behavior.  Some of these work around bugs in
       other implementations and are on by default.  You can use the  tls_dis-
       able_workarounds  parameter  to  selectively disable some or all of the
       bug work-arounds, making OpenSSL more strict at the cost of  non-inter-
       operability with SSL clients or servers that exhibit the bugs.

       Other  options are off by default, and typically enable or disable fea-
       tures rather than bug work-arounds.  These may be turned on (with care)
       via the tls_ssl_options parameter.  The value is a white-space or comma
       separated list of named options chosen from the list below.  The  names
       are  not case-sensitive, you can use lower-case if you prefer.  The up-
       per case values below match the corresponding macro name in  the  ssl.h
       header  file with the SSL_OP_ prefix removed.  It is possible that your
       OpenSSL version includes new options added after  your  Postfix  source
       code  was  last  updated, in that case you can only enable one of these
       via the hexadecimal syntax below.

       You should only enable features via the hexadecimal mask when the  need
       to control the feature is critical (to deal with a new vulnerability or
       a serious interoperability problem).  Postfix DOES  NOT  promise  back-
       wards compatible behavior with respect to the mask bits.  A feature en-
       abled via the mask in one release may be enabled by other  means  in  a
       later  release,  and the mask bit will then be ignored.  Therefore, use
       of the hexadecimal mask is only a temporary measure until a new Postfix
       or OpenSSL release provides a better solution.

       If  the  value  of the parameter is a hexadecimal long integer starting
       with "0x", the options corresponding to the bits specified in its value
       are  enabled  (see  openssl/ssl.h and SSL_CTX_set_options(3)).  You can
       only enable options not already controlled by other  Postfix  settings.
       For example, you cannot disable protocols or enable server cipher pref-
       erence.  Do not attempt to turn all features by specifying  0xFFFFFFFF,
       this  is  unlikely  to  be a good idea.  Some bug work-arounds are also
       valid here, allowing them to be re-enabled if/when  they're  no  longer
       enabled by default.  The supported values include:

       ENABLE_MIDDLEBOX_COMPAT
              Postfix >= 3.4. See SSL_CTX_set_options(3).

       LEGACY_SERVER_CONNECT
              See SSL_CTX_set_options(3).

       NO_TICKET
              Enabled  by default when needed in fully-patched Postfix >= 2.7.
              Not needed at all for Postfix >= 2.11, unless  for  some  reason
              you do not want to support TLS session resumption.  Best not set
              explicitly.  See SSL_CTX_set_options(3).

       NO_COMPRESSION
              Disable SSL compression even if supported  by  the  OpenSSL  li-
              brary.  Compression is CPU-intensive, and compression before en-
              cryption does not always improve security.

       NO_RENEGOTIATION
              Postfix >= 3.4.  This can reduce opportunities for  a  potential
              CPU exhaustion attack.  See SSL_CTX_set_options(3).

       NO_SESSION_RESUMPTION_ON_RENEGOTIATION
              Postfix >= 3.4. See SSL_CTX_set_options(3).

       PRIORITIZE_CHACHA
              Postfix >= 3.4. See SSL_CTX_set_options(3).

       This feature is available in Postfix 2.11 and later.

tls_wildcard_matches_multiple_labels (default: yes)
       Match multiple DNS labels with "*" in wildcard certificates.

       Some  mail service providers prepend the customer domain name to a base
       domain for which they have a wildcard TLS  certificate.   For  example,
       the MX records for example.com hosted by example.net may be:

           example.com. IN MX 0 example.com.mx1.example.net.
           example.com. IN MX 0 example.com.mx2.example.net.

       and the TLS certificate may be for "*.example.net". The "*" then corre-
       sponds with multiple labels in the  mail  server  domain  name.   While
       multi-label  wildcards are not widely supported, and are not blessed by
       any standard, there is little to be gained by disallowing their use  in
       this context.

       Notes:

       o      In  a  certificate name, the "*" is special only when it is used
              as the first label.

       o      While Postfix (2.11 or later) can match "*" with multiple domain
              name labels, other implementations likely will not.

       o      Earlier   Postfix   implementations   behave  as  if  "tls_wild-
              card_matches_multiple_labels = no".

       This feature is available in Postfix 2.11 and later.

tlsmgr_service_name (default: tlsmgr)
       The name of the tlsmgr(8) service  entry  in  master.cf.  This  service
       maintains TLS session caches and other information in support of TLS.

       This feature is available in Postfix 2.11 and later.

tlsproxy_client_CAfile (default: $smtp_tls_CAfile)
       A  file  containing  CA certificates of root CAs trusted to sign either
       remote TLS server certificates or intermediate  CA  certificates.   See
       smtp_tls_CAfile for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_CApath (default: $smtp_tls_CApath)
       Directory with PEM format Certification Authority certificates that the
       Postfix tlsproxy(8) client uses to verify a remote TLS server  certifi-
       cate. See smtp_tls_CApath for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_cert_file (default: $smtp_tls_cert_file)
       File with the Postfix tlsproxy(8) client RSA certificate in PEM format.
       See smtp_tls_cert_file for further details.  The preferred way to  con-
       figure   tlsproxy   client  keys  and  certificates  is  via  the  "tl-
       sproxy_client_chain_files" parameter.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_chain_files (default: $smtp_tls_chain_files)
       Files with the Postfix tlsproxy(8) client keys and  certificate  chains
       in PEM format. See smtp_tls_chain_files for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_dcert_file (default: $smtp_tls_dcert_file)
       File with the Postfix tlsproxy(8) client DSA certificate in PEM format.
       See smtp_tls_dcert_file for further details. DSA is obsolete and should
       not be used.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_dkey_file (default: $smtp_tls_dkey_file)
       File with the Postfix tlsproxy(8) client DSA private key in PEM format.
       See smtp_tls_dkey_file for further details. DSA is obsolete and  should
       not be used.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_eccert_file (default: $smtp_tls_eccert_file)
       File  with the Postfix tlsproxy(8) client ECDSA certificate in PEM for-
       mat. See smtp_tls_eccert_file for further details. The preferred way to
       configure  tlsproxy  client  keys  and  certificates  is  via  the "tl-
       sproxy_client_chain_files" parameter.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_eckey_file (default: $smtp_tls_eckey_file)
       File with the Postfix tlsproxy(8) client ECDSA private key in PEM  for-
       mat. See smtp_tls_eckey_file for further details.  The preferred way to
       configure tlsproxy  client  keys  and  certificates  is  via  the  "tl-
       sproxy_client_chain_files" parameter.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_enforce_tls (default: $smtp_enforce_tls)
       Enforcement  mode:  require  that SMTP servers use TLS encryption.  See
       smtp_enforce_tls for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_fingerprint_digest (default: $smtp_tls_fingerprint_digest)
       The message digest algorithm used to construct remote TLS  server  cer-
       tificate  fingerprints. See smtp_tls_fingerprint_digest for further de-
       tails.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_key_file (default: $smtp_tls_key_file)
       File with the Postfix tlsproxy(8) client RSA private key in PEM format.
       See smtp_tls_key_file for further details. The preferred way to config-
       ure  tlsproxy  client  keys  and   certificates   is   via   the   "tl-
       sproxy_client_chain_files" parameter.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_loglevel (default: $smtp_tls_loglevel)
       Enable  additional  Postfix tlsproxy(8) client logging of TLS activity.
       See smtp_tls_loglevel for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_loglevel_parameter (default: smtp_tls_loglevel)
       The name of the parameter that  provides  the  tlsproxy_client_loglevel
       value.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_per_site (default: $smtp_tls_per_site)
       Optional  lookup  tables  with the Postfix tlsproxy(8) client TLS usage
       policy by next-hop destination and by remote TLS server hostname.   See
       smtp_tls_per_site for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_policy_maps (default: $smtp_tls_policy_maps)
       Optional lookup tables with the Postfix tlsproxy(8) client TLS security
       policy by next-hop destination. See  smtp_tls_policy_maps  for  further
       details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_scert_verifydepth (default: $smtp_tls_scert_verifydepth)
       The  verification  depth  for  remote  TLS  server  certificates.   See
       smtp_tls_scert_verifydepth for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_security_level (default: $smtp_tls_security_level)
       The default TLS security level for the Postfix tlsproxy(8) client.  See
       smtp_tls_security_level for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_client_use_tls (default: $smtp_use_tls)
       Opportunistic mode: use TLS when a remote server announces TLS support.
       See smtp_use_tls for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory TLS: announce STARTTLS support to remote  SMTP  clients,  and
       require that clients use TLS encryption. See smtpd_enforce_tls for fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_service_name (default: tlsproxy)
       The name of the tlsproxy(8) service entry in  master.cf.  This  service
       performs plaintext <=> TLS ciphertext conversion.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CAfile (default: $smtpd_tls_CAfile)
       A  file  containing (PEM format) CA certificates of root CAs trusted to
       sign either remote SMTP client certificates or intermediate CA certifi-
       cates.  See smtpd_tls_CAfile for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CApath (default: $smtpd_tls_CApath)
       A directory containing (PEM format) CA certificates of root CAs trusted
       to sign either remote SMTP client certificates or intermediate CA  cer-
       tificates. See smtpd_tls_CApath for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_always_issue_session_ids  (default:  $smtpd_tls_always_issue_ses-
       sion_ids)
       Force the Postfix tlsproxy(8) server to issue a TLS  session  id,  even
       when TLS session caching is turned off. See smtpd_tls_always_issue_ses-
       sion_ids for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ask_ccert (default: $smtpd_tls_ask_ccert)
       Ask  a   remote   SMTP   client   for   a   client   certificate.   See
       smtpd_tls_ask_ccert for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ccert_verifydepth (default: $smtpd_tls_ccert_verifydepth)
       The  verification depth for remote SMTP client certificates. A depth of
       1 is sufficient if the issuing CA is listed in a  local  CA  file.  See
       smtpd_tls_ccert_verifydepth for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_cert_file (default: $smtpd_tls_cert_file)
       File with the Postfix tlsproxy(8) server RSA certificate in PEM format.
       This file may also contain the Postfix tlsproxy(8) server  private  RSA
       key.  See smtpd_tls_cert_file for further details.  With Postfix >= 3.4
       the preferred way to configure tlsproxy server keys and certificates is
       via the "tlsproxy_tls_chain_files" parameter.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_chain_files (default: $smtpd_tls_chain_files)
       Files  with  the Postfix tlsproxy(8) server keys and certificate chains
       in PEM format. See smtpd_tls_chain_files for further details.

       This feature is available in Postfix 3.4 and later.

tlsproxy_tls_ciphers (default: $smtpd_tls_ciphers)
       The minimum TLS cipher grade that the Postfix tlsproxy(8)  server  will
       use  with  opportunistic TLS encryption. See smtpd_tls_ciphers for fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dcert_file (default: $smtpd_tls_dcert_file)
       File with the Postfix tlsproxy(8) server DSA certificate in PEM format.
       This  file  may also contain the Postfix tlsproxy(8) server private DSA
       key.  DSA is obsolete and should not be used.  See smtpd_tls_dcert_file
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh1024_param_file (default: $smtpd_tls_dh1024_param_file)
       File  with DH parameters that the Postfix tlsproxy(8) server should use
       with non-export EDH ciphers. See smtpd_tls_dh1024_param_file  for  fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh512_param_file (default: $smtpd_tls_dh512_param_file)
       File  with DH parameters that the Postfix tlsproxy(8) server should use
       with export-grade EDH ciphers. See smtpd_tls_dh512_param_file for  fur-
       ther  details.   The  default SMTP server cipher grade is "medium" with
       Postfix releases after the middle of 2015, and as a result export-grade
       cipher suites are by default not used.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dkey_file (default: $smtpd_tls_dkey_file)
       File with the Postfix tlsproxy(8) server DSA private key in PEM format.
       This file may be combined with the Postfix tlsproxy(8) server DSA  cer-
       tificate  file  specified  with $smtpd_tls_dcert_file.  DSA is obsolete
       and should not be used.  See smtpd_tls_dkey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eccert_file (default: $smtpd_tls_eccert_file)
       File with the Postfix tlsproxy(8) server ECDSA certificate in PEM  for-
       mat.  This file may also contain the Postfix tlsproxy(8) server private
       ECDSA key.  See smtpd_tls_eccert_file for further details.  With  Post-
       fix >= 3.4 the preferred way to configure tlsproxy server keys and cer-
       tificates is via the "tlsproxy_tls_chain_files" parameter.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eckey_file (default: $smtpd_tls_eckey_file)
       File with the Postfix tlsproxy(8) server ECDSA private key in PEM  for-
       mat.   This  file  may  be combined with the Postfix tlsproxy(8) server
       ECDSA certificate  file  specified  with  $smtpd_tls_eccert_file.   See
       smtpd_tls_eckey_file for further details.  With Postfix >= 3.4 the pre-
       ferred way to configure tlsproxy server keys and  certificates  is  via
       the "tlsproxy_tls_chain_files" parameter.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eecdh_grade (default: $smtpd_tls_eecdh_grade)
       The  Postfix  tlsproxy(8)  server  security  grade for ephemeral ellip-
       tic-curve     Diffie-Hellman     (EECDH)     key     exchange.      See
       smtpd_tls_eecdh_grade for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_exclude_ciphers (default: $smtpd_tls_exclude_ciphers)
       List  of ciphers or cipher types to exclude from the tlsproxy(8) server
       cipher list at all TLS security levels.  See  smtpd_tls_exclude_ciphers
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_fingerprint_digest (default: $smtpd_tls_fingerprint_digest)
       The  message  digest algorithm to construct remote SMTP client-certifi-
       cate fingerprints. See  smtpd_tls_fingerprint_digest  for  further  de-
       tails.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_key_file (default: $smtpd_tls_key_file)
       File with the Postfix tlsproxy(8) server RSA private key in PEM format.
       This file may be combined with the Postfix tlsproxy(8) server RSA  cer-
       tificate     file    specified    with    $smtpd_tls_cert_file.     See
       smtpd_tls_key_file for further details.  With Postfix >= 3.4  the  pre-
       ferred  way  to  configure tlsproxy server keys and certificates is via
       the "tlsproxy_tls_chain_files" parameter.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_loglevel (default: $smtpd_tls_loglevel)
       Enable additional Postfix tlsproxy(8) server logging of  TLS  activity.
       Each  logging  level  also includes the information that is logged at a
       lower logging level. See smtpd_tls_loglevel for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_ciphers (default: $smtpd_tls_mandatory_ciphers)
       The minimum TLS cipher grade that the Postfix tlsproxy(8)  server  will
       use  with mandatory TLS encryption. See smtpd_tls_mandatory_ciphers for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_exclude_ciphers   (default:    $smtpd_tls_mandatory_ex-
       clude_ciphers)
       Additional  list  of  ciphers  or  cipher types to exclude from the tl-
       sproxy(8) server cipher list at mandatory  TLS  security  levels.   See
       smtpd_tls_mandatory_exclude_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_protocols (default: $smtpd_tls_mandatory_protocols)
       The  SSL/TLS  protocols accepted by the Postfix tlsproxy(8) server with
       mandatory TLS encryption. If the list is empty, the server supports all
       available SSL/TLS protocol versions.  See smtpd_tls_mandatory_protocols
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_protocols (default: $smtpd_tls_protocols)
       List of TLS protocols that the Postfix tlsproxy(8) server will  exclude
       or  include  with opportunistic TLS encryption. See smtpd_tls_protocols
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_req_ccert (default: $smtpd_tls_req_ccert)
       With mandatory TLS encryption, require a  trusted  remote  SMTP  client
       certificate  in  order  to  allow  TLS  connections  to  proceed.   See
       smtpd_tls_req_ccert for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_security_level (default: $smtpd_tls_security_level)
       The SMTP TLS security level for the Postfix tlsproxy(8) server; when  a
       non-empty  value  is  specified, this overrides the obsolete parameters
       smtpd_use_tls and smtpd_enforce_tls. See  smtpd_tls_security_level  for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_session_cache_timeout (default: $smtpd_tls_session_cache_timeout)

       Obsolete expiration time of  Postfix  tlsproxy(8)  server  TLS  session
       cache  information. Since the cache is shared with smtpd(8) and managed
       by tlsmgr(8), there is only one expiration time  for  the  SMTP  server
       cache   shared   by   all   three   services,   namely   smtpd_tls_ses-
       sion_cache_timeout.

       This feature is available in Postfix 2.8 and later.

tlsproxy_use_tls (default: $smtpd_use_tls)
       Opportunistic TLS: announce STARTTLS support to  remote  SMTP  clients,
       but  do  not require that clients use TLS encryption. See smtpd_use_tls
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_watchdog_timeout (default: 10s)
       How much time a tlsproxy(8) process may take to process local or remote
       I/O  before  it  is terminated by a built-in watchdog timer.  This is a
       safety mechanism that prevents tlsproxy(8) from becoming non-responsive
       due  to  a bug in Postfix itself or in system software.  To avoid false
       alarms and unnecessary cache corruption this limit cannot be set  under
       10s.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8 and later

trace_service_name (default: trace)
       The  name  of  the  trace  service.  This service is implemented by the
       bounce(8) daemon and maintains a record of mail deliveries and produces
       a  mail  delivery report when verbose delivery is requested with "send-
       mail -v".

       This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)
       A transport-specific override for the default_delivery_slot_cost param-
       eter value, where transport is the master.cf name of the message deliv-
       ery transport.

       Note: transport_delivery_slot_cost  parameters  will  not  show  up  in
       "postconf"  command output before Postfix version 2.9.  This limitation
       applies to many parameters whose name is a combination of  a  master.cf
       service   name   and   a   built-in  suffix  (in  this  case:  "_deliv-
       ery_slot_cost").

transport_delivery_slot_discount (default: $default_delivery_slot_discount)
       A transport-specific override  for  the  default_delivery_slot_discount
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       Note: transport_delivery_slot_discount parameters will not show  up  in
       "postconf"  command output before Postfix version 2.9.  This limitation
       applies to many parameters whose name is a combination of  a  master.cf
       service  name and a built-in suffix (in this case: "_delivery_slot_dis-
       count").

transport_delivery_slot_loan (default: $default_delivery_slot_loan)
       A transport-specific override for the default_delivery_slot_loan param-
       eter value, where transport is the master.cf name of the message deliv-
       ery transport.

       Note: transport_delivery_slot_loan  parameters  will  not  show  up  in
       "postconf"  command output before Postfix version 2.9.  This limitation
       applies to many parameters whose name is a combination of  a  master.cf
       service   name   and   a   built-in  suffix  (in  this  case:  "_deliv-
       ery_slot_loan").

transport_destination_concurrency_failed_cohort_limit (default:  $default_des-
       tination_concurrency_failed_cohort_limit)
       A   transport-specific  override  for  the  default_destination_concur-
       rency_failed_cohort_limit parameter value, where transport is the  mas-
       ter.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_failed_cohort_limit param-
       eters will not show up in "postconf" command output before Postfix ver-
       sion  2.9.   This limitation applies to many parameters whose name is a
       combination of a master.cf service name and a built-in suffix (in  this
       case: "_destination_concurrency_failed_cohort_limit").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concur-
       rency_limit)
       A  transport-specific  override  for  the   default_destination_concur-
       rency_limit  parameter  value, where transport is the master.cf name of
       the message delivery transport.

       Note: some transport_destination_concurrency_limit parameters will  not
       show  up in "postconf" command output before Postfix version 2.9.  This
       limitation applies to many parameters whose name is a combination of  a
       master.cf  service name and a built-in suffix (in this case: "_destina-
       tion_concurrency_limit").

transport_destination_concurrency_negative_feedback (default:  $default_desti-
       nation_concurrency_negative_feedback)
       A   transport-specific  override  for  the  default_destination_concur-
       rency_negative_feedback parameter value, where transport  is  the  mas-
       ter.cf name of the message delivery transport.

       Note:  some transport_destination_concurrency_negative_feedback parame-
       ters will not show up in "postconf" command output before Postfix  ver-
       sion  2.9.   This limitation applies to many parameters whose name is a
       combination of a master.cf service name and a built-in suffix (in  this
       case: "_destination_concurrency_negative_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback  (default: $default_desti-
       nation_concurrency_positive_feedback)
       A  transport-specific  override  for  the   default_destination_concur-
       rency_positive_feedback  parameter  value,  where transport is the mas-
       ter.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_positive_feedback  parame-
       ters  will not show up in "postconf" command output before Postfix ver-
       sion 2.9.  This limitation applies to many parameters whose name  is  a
       combination  of a master.cf service name and a built-in suffix (in this
       case: "_destination_concurrency_positive_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)
       A transport-specific override  for  the  default_destination_rate_delay
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       Note: some transport_destination_rate_delay parameters will not show up
       in  "postconf" command output before Postfix version 2.9.  This limita-
       tion applies to many parameters whose name is a combination of  a  mas-
       ter.cf  service  name  and  a built-in suffix (in this case: "_destina-
       tion_rate_delay").

       This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit  (default:  $default_destination_recipi-
       ent_limit)
       A   transport-specific  override  for  the  default_destination_recipi-
       ent_limit parameter value, where transport is the master.cf name of the
       message delivery transport.

       Note:  some  transport_destination_recipient_limit  parameters will not
       show up in "postconf" command output before Postfix version 2.9.   This
       limitation  applies to many parameters whose name is a combination of a
       master.cf service name and a built-in suffix (in this case:  "_destina-
       tion_recipient_limit").

transport_extra_recipient_limit (default: $default_extra_recipient_limit)
       A transport-specific override for the default_extra_recipient_limit pa-
       rameter value, where transport is the master.cf name of the message de-
       livery transport.

       Note:  transport_extra_recipient_limit  parameters  will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service name and a  built-in  suffix  (in  this  case:  "_extra_recipi-
       ent_limit").

transport_initial_destination_concurrency  (default: $initial_destination_con-
       currency)
       A transport-specific override for  the  initial_destination_concurrency
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       Note: some  transport_initial_destination_concurrency  parameters  will
       not  show  up  in "postconf" command output before Postfix version 2.9.
       This limitation applies to many parameters whose name is a  combination
       of a master.cf service name and a built-in suffix (in this case: "_ini-
       tial_destination_concurrency").

       This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)
       Optional lookup tables with mappings from recipient address to (message
       delivery  transport,  next-hop  destination).  See transport(5) for de-
       tails.

       Specify zero or more "type:table" lookup tables,  separated  by  white-
       space  or comma. Tables will be searched in the specified order until a
       match is found.  If you use this feature with local files, run "postmap
       /etc/postfix/transport" after making a change.

       Pattern  matching  of domain names is controlled by the presence or ab-
       sence of "transport_maps" in the  parent_domain_matches_subdomains  pa-
       rameter value.

       For safety reasons, as of Postfix 2.3 this feature does not allow $num-
       ber substitutions in regular expression maps.

       Examples:

       transport_maps = dbm:/etc/postfix/transport
       transport_maps = hash:/etc/postfix/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
       A transport-specific override  for  the  default_minimum_delivery_slots
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       Note: transport_minimum_delivery_slots parameters will not show  up  in
       "postconf"  command output before Postfix version 2.9.  This limitation
       applies to many parameters whose name is a combination of  a  master.cf
       service  name  and  a  built-in  suffix (in this case: "_minimum_deliv-
       ery_slots").

transport_recipient_limit (default: $default_recipient_limit)
       A transport-specific override for the default_recipient_limit parameter
       value,  where  transport  is the master.cf name of the message delivery
       transport.

       Note: some transport_recipient_limit parameters will  not  show  up  in
       "postconf"  command output before Postfix version 2.9.  This limitation
       applies to many parameters whose name is a combination of  a  master.cf
       service name and a built-in suffix (in this case: "_recipient_limit").

transport_recipient_refill_delay (default: $default_recipient_refill_delay)
       A  transport-specific  override  for the default_recipient_refill_delay
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  transport_recipient_refill_delay  parameters will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service name and a  built-in  suffix  (in  this  case:  "_recipient_re-
       fill_delay").

       This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)
       A  transport-specific  override  for the default_recipient_refill_limit
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  transport_recipient_refill_limit  parameters will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service name and a  built-in  suffix  (in  this  case:  "_recipient_re-
       fill_limit").

       This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)
       The  time  between  attempts  by the Postfix queue manager to contact a
       malfunctioning message delivery transport.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

transport_time_limit (default: $command_time_limit)
       A  transport-specific  override  for  the  command_time_limit parameter
       value, where transport is the master.cf name of  the  message  delivery
       transport.

       Note:  transport_time_limit  parameters  will not show up in "postconf"
       command output before Postfix version 2.9.  This limitation applies  to
       many parameters whose name is a combination of a master.cf service name
       and a built-in suffix (in this case: "_time_limit").

transport_transport_rate_delay (default: $default_transport_rate_delay)
       A transport-specific override for the default_transport_rate_delay  pa-
       rameter value, where the initial transport in the parameter name is the
       master.cf name of the message delivery transport.

trigger_timeout (default: 10s)
       The time limit for sending a trigger to a Postfix daemon (for  example,
       the  pickup(8)  or  qmgr(8)  daemon). This time limit prevents programs
       from getting stuck when the mail system is under heavy load.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

undisclosed_recipients_header (default: see postconf -d output)
       Message  header  that the Postfix cleanup(8) server inserts when a mes-
       sage contains no To: or Cc: message header. With Postfix 2.8 and later,
       the  default  value  is  empty.  With Postfix 2.4-2.7, specify an empty
       value to disable this feature.

       Example:

       # Default value before Postfix 2.8.
       # Note: the ":" and ";" are both required.
       undisclosed_recipients_header = To: undisclosed-recipients:;

unknown_address_reject_code (default: 450)
       The numerical response code when the  Postfix  SMTP  server  rejects  a
       sender or recipient address because its domain is unknown.  This is one
       of the possible replies from the restrictions reject_unknown_sender_do-
       main and reject_unknown_recipient_domain.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

unknown_address_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when  reject_unknown_sender_domain  or
       reject_unknown_recipient_domain  fail  due  to a temporary error condi-
       tion. Specify "defer" to defer the remote SMTP client  request  immedi-
       ately.  With  the  default  "defer_if_permit"  action, the Postfix SMTP
       server continues to look for opportunities to reject mail,  and  defers
       the client request only if it would otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_client_reject_code (default: 450)
       The  numerical  Postfix SMTP server response code when a client without
       valid  address  <=>  name  mapping  is  rejected  by   the   reject_un-
       known_client_hostname  restriction. The SMTP server always replies with
       450 when the mapping failed due to a temporary error condition.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)
       The  Postfix  SMTP  server's  action  when reject_unknown_helo_hostname
       fails due to a temporary error condition. Specify "defer" to defer  the
       remote SMTP client request immediately. With the default "defer_if_per-
       mit" action, the Postfix SMTP server continues to look  for  opportuni-
       ties  to  reject  mail,  and defers the client request only if it would
       otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_hostname_reject_code (default: 450)
       The numerical Postfix SMTP server response code when the hostname spec-
       ified  with  the  HELO  or  EHLO  command is rejected by the reject_un-
       known_helo_hostname restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

unknown_local_recipient_reject_code (default: 550)
       The  numerical  Postfix  SMTP server response code when a recipient ad-
       dress is local, and $local_recipient_maps specifies a  list  of  lookup
       tables that does not match the recipient.  A recipient address is local
       when its domain matches $mydestination, $proxy_interfaces or  $inet_in-
       terfaces.

       The  default  setting is 550 (reject mail) but it is safer to initially
       use 450 (try again later) so you have time to  find  out  if  your  lo-
       cal_recipient_maps settings are OK.

       Example:

       unknown_local_recipient_reject_code = 450

       This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
       The  numerical  Postfix SMTP server reply code when a recipient address
       matches $relay_domains, and relay_recipient_maps specifies  a  list  of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
       The  Postfix  SMTP  server  reply code when a recipient address matches
       $virtual_alias_domains, and $virtual_alias_maps  specifies  a  list  of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
       The  Postfix  SMTP  server  reply code when a recipient address matches
       $virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unverified_recipient_defer_code (default: 450)
       The  numerical  Postfix  SMTP  server response when a recipient address
       probe fails due to a temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

       This feature is available in Postfix 2.6 and later.

unverified_recipient_reject_code (default: 450)
       The numerical Postfix SMTP server response when a recipient address  is
       rejected by the reject_unverified_recipient restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.1 and later.

unverified_recipient_reject_reason (default: empty)
       The Postfix SMTP server's reply when rejecting mail with reject_unveri-
       fied_recipient. Do not include the numeric SMTP reply code or  the  en-
       hanced  status  code.  By default, the response includes actual address
       verification details.

       Example:

       unverified_recipient_reject_reason = Recipient address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_recipient_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when reject_unverified_recipient fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP client request immediately. With the default "defer_if_permit" ac-
       tion,  the  Postfix  SMTP server continues to look for opportunities to
       reject mail, and defers the client request only if it  would  otherwise
       be accepted.

       This feature is available in Postfix 2.6 and later.

unverified_sender_defer_code (default: 450)
       The  numerical  Postfix SMTP server response code when a sender address
       probe fails due to a temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

       This feature is available in Postfix 2.6 and later.

unverified_sender_reject_code (default: 450)
       The numerical Postfix SMTP server response code when  a  recipient  ad-
       dress is rejected by the reject_unverified_sender restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.1 and later.

unverified_sender_reject_reason (default: empty)
       The Postfix SMTP server's reply when rejecting mail with reject_unveri-
       fied_sender. Do not include the numeric SMTP reply code or the enhanced
       status code. By default, the response includes actual address verifica-
       tion details.

       Example:

       unverified_sender_reject_reason = Sender address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_sender_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action  when  reject_unverified_sender  fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP client request immediately. With the default "defer_if_permit" ac-
       tion,  the  Postfix  SMTP server continues to look for opportunities to
       reject mail, and defers the client request only if it  would  otherwise
       be accepted.

       This feature is available in Postfix 2.6 and later.

verp_delimiter_filter (default: -=+)
       The  characters  Postfix  accepts  as  VERP delimiter characters on the
       Postfix sendmail(1) command line and in SMTP commands.

       This feature is available in Postfix 1.1 and later.

virtual_alias_address_length_limit (default: 1000)
       The maximal length of an email address after virtual  alias  expansion.
       This  stops virtual aliasing loops that increase the address length ex-
       ponentially.

       This feature is available in Postfix 3.0 and later.

virtual_alias_domains (default: $virtual_alias_maps)
       Postfix is final destination for the specified list  of  virtual  alias
       domains,  that  is,  domains for which all addresses are aliased to ad-
       dresses in other local or remote domains. The SMTP server validates re-
       cipient addresses with $virtual_alias_maps and rejects non-existent re-
       cipients.  See  also  the  virtual  alias  domain  class  in  the   AD-
       DRESS_CLASS_README file

       This  feature  is available in Postfix 2.0 and later. The default value
       is backwards compatible with Postfix version 1.1.

       The default value is $virtual_alias_maps so that you can keep  all  in-
       formation  about  virtual alias domains in one place.  If you have many
       users, it is better to separate  information  that  changes  more  fre-
       quently  (virtual  address -> local or remote address mapping) from in-
       formation that changes less frequently  (the  list  of  virtual  domain
       names).

       Specify  a  list  of host or domain names, "/file/name" or "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is  replaced  by  its  contents; a "type:table" lookup table is matched
       when a table entry matches a lookup string (the lookup  result  is  ig-
       nored).  Continue long lines by starting the next line with whitespace.
       Specify "!pattern" to exclude a host or domain name from the list.  The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       See also the VIRTUAL_README and ADDRESS_CLASS_README documents for fur-
       ther information.

       Example:

       virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
       The maximal number of addresses that virtual alias  expansion  produces
       from each original recipient.

       This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
       Optional lookup tables that alias specific mail addresses or domains to
       other local or remote address.  The table format and lookups are  docu-
       mented  in virtual(5). For an overview of Postfix address manipulations
       see the ADDRESS_REWRITING_README document.

       This feature is available in Postfix 2.0 and later. The  default  value
       is backwards compatible with Postfix version 1.1.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.  Note: these lookups are recursive.

       If  you  use  this  feature with indexed files, run "postmap /etc/post-
       fix/virtual" after changing the file.

       Examples:

       virtual_alias_maps = dbm:/etc/postfix/virtual
       virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)
       The maximal nesting depth of virtual alias  expansion.   Currently  the
       recursion  limit  is  applied  only to the left branch of the expansion
       graph, so the depth of the tree can in the worst case reach the sum  of
       the expansion and recursion limits.  This may change in the future.

       This feature is available in Postfix 2.1 and later.

virtual_delivery_status_filter (default: $default_delivery_status_filter)
       Optional  filter for the virtual(8) delivery agent to change the deliv-
       ery status code or explanatory text of successful or  unsuccessful  de-
       liveries.  See default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

virtual_destination_concurrency_limit  (default:  $default_destination_concur-
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  virtual  message delivery transport. This limit is enforced by the
       queue manager. The message delivery transport name is the  first  field
       in the entry in the master.cf file.

virtual_destination_recipient_limit   (default:   $default_destination_recipi-
       ent_limit)
       The maximal number of recipients per message for  the  virtual  message
       delivery  transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting  this  parameter  to  a  value of 1 changes the meaning of vir-
       tual_destination_concurrency_limit from  concurrency  per  domain  into
       concurrency per recipient.

virtual_gid_maps (default: empty)
       Lookup  tables  with  the per-recipient group ID for virtual(8) mailbox
       delivery.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       In a lookup table, specify a left-hand side of "@domain.tld"  to  match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "user@domain.tld" entry.

       When  a  recipient  address   has   an   optional   address   extension
       (user+foo@domain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:  for  security  reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open the table directly. Before Postfix version 2.2, the virtual(8) de-
       livery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
       A prefix that the virtual(8) delivery agent prepends  to  all  pathname
       results  from  $virtual_mailbox_maps  table  lookups.  This is a safety
       measure to ensure that an out of control map doesn't  litter  the  file
       system with mailboxes.  While virtual_mailbox_base could be set to "/",
       this setting isn't recommended.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       Example:

       virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
       Postfix is final destination for the specified list of domains; mail is
       delivered  via  the $virtual_transport mail delivery transport.  By de-
       fault this is the Postfix virtual(8) delivery agent.  The  SMTP  server
       validates  recipient  addresses  with $virtual_mailbox_maps and rejects
       mail for non-existent recipients.  See also the virtual mailbox  domain
       class in the ADDRESS_CLASS_README file.

       This  parameter expects the same syntax as the mydestination configura-
       tion parameter.

       This feature is available in Postfix 2.0 and later. The  default  value
       is backwards compatible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
       The  maximal  size  in  bytes  of  an  individual virtual(8) mailbox or
       maildir file, or zero (no limit).

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

virtual_mailbox_lock (default: see postconf -d output)
       How to lock a UNIX-style virtual(8) mailbox before attempting delivery.
       For  a  list  of  available file locking methods, use the "postconf -l"
       command.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       This setting is ignored with maildir style delivery, because  such  de-
       liveries are safe without application-level locks.

       Note  1:  the dotlock method requires that the recipient UID or GID has
       write access to the parent directory of the recipient's mailbox file.

       Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
       Optional lookup tables with all valid addresses  in  the  domains  that
       match $virtual_mailbox_domains.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       In  a  lookup table, specify a left-hand side of "@domain.tld" to match
       any user in  the  specified  domain  that  does  not  have  a  specific
       "user@domain.tld" entry.

       The  remainder  of  this  text  is  specific to the virtual(8) delivery
       agent.  It does not apply when mail is delivered with a different  mail
       delivery program.

       The virtual(8) delivery agent uses this table to look up the per-recip-
       ient mailbox or maildir pathname.  If the lookup result ends in a slash
       ("/"), maildir-style delivery is carried out, otherwise the path is as-
       sumed to specify a UNIX-style mailbox file.  Note  that  $virtual_mail-
       box_base is unconditionally prepended to this path.

       When   a   recipient   address   has   an  optional  address  extension
       (user+foo@domain.tld), the virtual(8) delivery agent looks up the  full
       address  first,  and  when the lookup fails, it looks up the unextended
       address (user@domain.tld).

       Note 1: for security reasons, the virtual(8) delivery  agent  disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note 2: for  security  reasons,  the  virtual(8)  delivery  agent  will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open the table directly. Before Postfix version 2.2, the virtual(8) de-
       livery agent will terminate with a fatal error.

virtual_maps (default: empty)
       Optional lookup tables with a) names of domains for which all addresses
       are aliased to addresses in other local or remote domains, and  b)  ad-
       dresses that are aliased to addresses in other local or remote domains.
       Available before Postfix version 2.0.  With  Postfix  version  2.0  and
       later, this is replaced by separate controls: virtual_alias_domains and
       virtual_alias_maps.

virtual_minimum_uid (default: 100)
       The minimum user ID value that the virtual(8) delivery agent accepts as
       a  result  from  $virtual_uid_maps  table lookup.  Returned values less
       than this will be rejected, and the message will be deferred.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

virtual_transport (default: virtual)
       The default mail delivery transport and next-hop destination for  final
       delivery  to domains listed with $virtual_mailbox_domains.  This infor-
       mation can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of  a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
       Lookup tables with the per-recipient user ID that the virtual(8) deliv-
       ery agent uses while writing to the recipient's mailbox.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       In a lookup table, specify a left-hand side of "@domain.tld"  to  match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "user@domain.tld" entry.

       When  a  recipient  address   has   an   optional   address   extension
       (user+foo@domain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:  for  security  reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open the table directly. Before Postfix version 2.2, the virtual(8) de-
       livery agent will terminate with a fatal error.

SEE ALSO
       postconf(1), Postfix configuration parameter maintenance
       master(5), Postfix daemon configuration maintenance

LICENSE
       The Secure Mailer license must be distributed with this software.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

       Viktor Dukhovni

                                                                   POSTCONF(5)

NAME | SYNOPSIS | DESCRIPTION | 2bounce_notice_recipient (default: postmaster) | access_map_defer_code (default: 450) | access_map_reject_code (default: 554) | address_verify_cache_cleanup_interval (default: 12h) | address_verify_default_transport (default: $default_transport) | address_verify_local_transport (default: $local_transport) | address_verify_map (default: see postconf -d output) | address_verify_negative_cache (default: yes) | address_verify_negative_expire_time (default: 3d) | address_verify_negative_refresh_time (default: 3h) | address_verify_pending_request_limit (default: see postconf -d output) | address_verify_poll_count (default: normal: 3, overload: 1) | address_verify_poll_delay (default: 3s) | address_verify_positive_expire_time (default: 31d) | address_verify_positive_refresh_time (default: 7d) | address_verify_relay_transport (default: $relay_transport) | address_verify_relayhost (default: $relayhost) | address_verify_sender (default: $double_bounce_sender) | address_verify_sender_dependent_default_transport_maps (default: $sender_de- | address_verify_sender_dependent_relayhost_maps (default: $sender_dependent_re- | address_verify_sender_ttl (default: 0s) | address_verify_service_name (default: verify) | address_verify_transport_maps (default: $transport_maps) | address_verify_virtual_transport (default: $virtual_transport) | alias_database (default: see postconf -d output) | alias_maps (default: see postconf -d output) | allow_mail_to_commands (default: alias, forward) | allow_mail_to_files (default: alias, forward) | allow_min_user (default: no) | allow_percent_hack (default: yes) | allow_untrusted_routing (default: no) | alternate_config_directories (default: empty) | always_add_missing_headers (default: no) | always_bcc (default: empty) | anvil_rate_time_unit (default: 60s) | anvil_status_update_time (default: 600s) | append_at_myorigin (default: yes) | append_dot_mydomain (default: Postfix >= 3.0: no, Postfix < 3.0: yes) | application_event_drain_time (default: 100s) | authorized_flush_users (default: static:anyone) | authorized_mailq_users (default: static:anyone) | authorized_submit_users (default: static:anyone) | authorized_verp_clients (default: $mynetworks) | backwards_bounce_logfile_compatibility (default: yes) | berkeley_db_create_buffer_size (default: 16777216) | berkeley_db_read_buffer_size (default: 131072) | best_mx_transport (default: empty) | biff (default: yes) | body_checks (default: empty) | body_checks_size_limit (default: 51200) | bounce_notice_recipient (default: postmaster) | bounce_queue_lifetime (default: 5d) | bounce_service_name (default: bounce) | bounce_size_limit (default: 50000) | bounce_template_file (default: empty) | broken_sasl_auth_clients (default: no) | canonical_classes (default: envelope_sender, envelope_recipient, | canonical_maps (default: empty) | cleanup_replace_stray_cr_lf (default: yes) | cleanup_service_name (default: cleanup) | command_directory (default: see postconf -d output) | command_execution_directory (default: empty) | command_expansion_filter (default: see postconf -d output) | command_time_limit (default: 1000s) | compatibility_level (default: 0) | config_directory (default: see postconf -d output) | confirm_delay_cleared (default: no) | connection_cache_protocol_timeout (default: 5s) | connection_cache_service_name (default: scache) | connection_cache_status_update_time (default: 600s) | connection_cache_ttl_limit (default: 2s) | content_filter (default: empty) | cyrus_sasl_config_path (default: empty) | daemon_directory (default: see postconf -d output) | daemon_table_open_error_is_fatal (default: no) | daemon_timeout (default: 18000s) | data_directory (default: see postconf -d output) | debug_peer_level (default: 2) | debug_peer_list (default: empty) | debugger_command (default: empty) | default_database_type (default: see postconf -d output) | default_delivery_slot_cost (default: 5) | default_delivery_slot_discount (default: 50) | default_delivery_slot_loan (default: 3) | default_delivery_status_filter (default: empty) | default_destination_concurrency_failed_cohort_limit (default: 1) | default_destination_concurrency_limit (default: 20) | default_destination_concurrency_negative_feedback (default: 1) | default_destination_concurrency_positive_feedback (default: 1) | default_destination_rate_delay (default: 0s) | default_destination_recipient_limit (default: 50) | default_extra_recipient_limit (default: 1000) | default_filter_nexthop (default: empty) | default_minimum_delivery_slots (default: 3) | default_privs (default: nobody) | default_process_limit (default: 100) | default_rbl_reply (default: see postconf -d output) | default_recipient_limit (default: 20000) | default_recipient_refill_delay (default: 5s) | default_recipient_refill_limit (default: 100) | default_transport (default: smtp) | default_transport_rate_delay (default: 0s) | default_verp_delimiters (default: +=) | defer_code (default: 450) | defer_service_name (default: defer) | defer_transports (default: empty) | delay_logging_resolution_limit (default: 2) | delay_notice_recipient (default: postmaster) | delay_warning_time (default: 0h) | deliver_lock_attempts (default: 20) | deliver_lock_delay (default: 1s) | destination_concurrency_feedback_debug (default: no) | detect_8bit_encoding_header (default: yes) | disable_dns_lookups (default: no) | disable_mime_input_processing (default: no) | disable_mime_output_conversion (default: no) | disable_verp_bounces (default: no) | disable_vrfy_command (default: no) | dns_ncache_ttl_fix_enable (default: no) | dnsblog_reply_delay (default: 0s) | dnsblog_service_name (default: dnsblog) | dont_remove (default: 0) | double_bounce_sender (default: double-bounce) | duplicate_filter_limit (default: 1000) | empty_address_default_transport_maps_lookup_key (default: <>) | empty_address_recipient (default: MAILER-DAEMON) | empty_address_relayhost_maps_lookup_key (default: <>) | enable_errors_to (default: no) | enable_idna2003_compatibility (default: no) | enable_long_queue_ids (default: no) | enable_original_recipient (default: yes) | error_notice_recipient (default: postmaster) | error_service_name (default: error) | execution_directory_expansion_filter (default: see postconf -d output) | expand_owner_alias (default: no) | export_environment (default: see postconf -d output) | extract_recipient_limit (default: 10240) | fallback_relay (default: empty) | fallback_transport (default: empty) | fallback_transport_maps (default: empty) | fast_flush_domains (default: $relay_domains) | fast_flush_purge_time (default: 7d) | fast_flush_refresh_time (default: 12h) | fault_injection_code (default: 0) | flush_service_name (default: flush) | fork_attempts (default: 5) | fork_delay (default: 1s) | forward_expansion_filter (default: see postconf -d output) | forward_path (default: see postconf -d output) | frozen_delivered_to (default: yes) | hash_queue_depth (default: 1) | hash_queue_names (default: deferred, defer) | header_address_token_limit (default: 10240) | header_checks (default: empty) | header_from_format (default: standard) | header_size_limit (default: 102400) | helpful_warnings (default: yes) | home_mailbox (default: empty) | hopcount_limit (default: 50) | html_directory (default: see postconf -d output) | ignore_mx_lookup_error (default: no) | import_environment (default: see postconf -d output) | in_flow_delay (default: 1s) | inet_interfaces (default: all) | inet_protocols (default: all) | initial_destination_concurrency (default: 5) | internal_mail_filter_classes (default: empty) | invalid_hostname_reject_code (default: 501) | ipc_idle (default: version dependent) | ipc_timeout (default: 3600s) | ipc_ttl (default: 1000s) | line_length_limit (default: 2048) | lmdb_map_size (default: 16777216) | lmtp_address_preference (default: ipv6) | lmtp_address_verify_target (default: rcpt) | lmtp_assume_final (default: no) | lmtp_balance_inet_protocols (default: yes) | lmtp_bind_address (default: empty) | lmtp_bind_address6 (default: empty) | lmtp_body_checks (default: empty) | lmtp_cache_connection (default: yes) | lmtp_cname_overrides_servername (default: yes) | lmtp_connect_timeout (default: 0s) | lmtp_connection_cache_destinations (default: empty) | lmtp_connection_cache_on_demand (default: yes) | lmtp_connection_cache_time_limit (default: 2s) | lmtp_connection_reuse_count_limit (default: 0) | lmtp_connection_reuse_time_limit (default: 300s) | lmtp_data_done_timeout (default: 600s) | lmtp_data_init_timeout (default: 120s) | lmtp_data_xfer_timeout (default: 180s) | lmtp_defer_if_no_mx_address_found (default: no) | lmtp_delivery_status_filter (default: empty) | lmtp_destination_concurrency_limit (default: $default_destination_concur- | lmtp_destination_recipient_limit (default: $default_destination_recipi- | lmtp_discard_lhlo_keyword_address_maps (default: empty) | lmtp_discard_lhlo_keywords (default: empty) | lmtp_dns_reply_filter (default: empty) | lmtp_dns_resolver_options (default: empty) | lmtp_dns_support_level (default: empty) | lmtp_enforce_tls (default: no) | lmtp_fallback_relay (default: empty) | lmtp_generic_maps (default: empty) | lmtp_header_checks (default: empty) | lmtp_host_lookup (default: dns) | lmtp_lhlo_name (default: $myhostname) | lmtp_lhlo_timeout (default: 300s) | lmtp_line_length_limit (default: 990) | lmtp_mail_timeout (default: 300s) | lmtp_mime_header_checks (default: empty) | lmtp_mx_address_limit (default: 5) | lmtp_mx_session_limit (default: 2) | lmtp_nested_header_checks (default: empty) | lmtp_per_record_deadline (default: no) | lmtp_pix_workaround_delay_time (default: 10s) | lmtp_pix_workaround_maps (default: empty) | lmtp_pix_workaround_threshold_time (default: 500s) | lmtp_pix_workarounds (default: empty) | lmtp_quit_timeout (default: 300s) | lmtp_quote_rfc821_envelope (default: yes) | lmtp_randomize_addresses (default: yes) | lmtp_rcpt_timeout (default: 300s) | lmtp_reply_filter (default: empty) | lmtp_rset_timeout (default: 20s) | lmtp_sasl_auth_cache_name (default: empty) | lmtp_sasl_auth_cache_time (default: 90d) | lmtp_sasl_auth_enable (default: no) | lmtp_sasl_auth_soft_bounce (default: yes) | lmtp_sasl_mechanism_filter (default: empty) | lmtp_sasl_password_maps (default: empty) | lmtp_sasl_path (default: empty) | lmtp_sasl_security_options (default: noplaintext, noanonymous) | lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options) | lmtp_sasl_tls_verified_security_options (default: $lmtp_sasl_tls_security_op- | lmtp_sasl_type (default: cyrus) | lmtp_send_dummy_mail_auth (default: no) | lmtp_send_xforward_command (default: no) | lmtp_sender_dependent_authentication (default: no) | lmtp_skip_5xx_greeting (default: yes) | lmtp_skip_quit_response (default: no) | lmtp_starttls_timeout (default: 300s) | lmtp_tcp_port (default: 24) | lmtp_tls_CAfile (default: empty) | lmtp_tls_CApath (default: empty) | lmtp_tls_block_early_mail_reply (default: empty) | lmtp_tls_cert_file (default: empty) | lmtp_tls_chain_files (default: empty) | lmtp_tls_ciphers (default: medium) | lmtp_tls_connection_reuse (default: no) | lmtp_tls_dcert_file (default: empty) | lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file) | lmtp_tls_eccert_file (default: empty) | lmtp_tls_eckey_file (default: empty) | lmtp_tls_enforce_peername (default: yes) | lmtp_tls_exclude_ciphers (default: empty) | lmtp_tls_fingerprint_cert_match (default: empty) | lmtp_tls_fingerprint_digest (default: md5) | lmtp_tls_force_insecure_host_tlsa_lookup (default: no) | lmtp_tls_key_file (default: $lmtp_tls_cert_file) | lmtp_tls_loglevel (default: 0) | lmtp_tls_mandatory_ciphers (default: medium) | lmtp_tls_mandatory_exclude_ciphers (default: empty) | lmtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3) | lmtp_tls_note_starttls_offer (default: no) | lmtp_tls_per_site (default: empty) | lmtp_tls_policy_maps (default: empty) | lmtp_tls_protocols (default: !SSLv2, !SSLv3) | lmtp_tls_scert_verifydepth (default: 9) | lmtp_tls_secure_cert_match (default: nexthop) | lmtp_tls_security_level (default: empty) | lmtp_tls_servername (default: empty) | lmtp_tls_session_cache_database (default: empty) | lmtp_tls_session_cache_timeout (default: 3600s) | lmtp_tls_trust_anchor_file (default: empty) | lmtp_tls_verify_cert_match (default: hostname) | lmtp_use_tls (default: no) | lmtp_xforward_timeout (default: 300s) | local_command_shell (default: empty) | local_delivery_status_filter (default: $default_delivery_status_filter) | local_destination_concurrency_limit (default: 2) | local_destination_recipient_limit (default: 1) | local_header_rewrite_clients (default: permit_inet_interfaces) | local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps) | local_transport (default: local:$myhostname) | luser_relay (default: empty) | mail_name (default: Postfix) | mail_owner (default: postfix) | mail_release_date (default: see postconf -d output) | mail_spool_directory (default: see postconf -d output) | mail_version (default: see postconf -d output) | mailbox_command (default: empty) | mailbox_command_maps (default: empty) | mailbox_delivery_lock (default: see postconf -d output) | mailbox_size_limit (default: 51200000) | mailbox_transport (default: empty) | mailbox_transport_maps (default: empty) | maillog_file (default: empty) | maillog_file_compressor (default: gzip) | maillog_file_prefixes (default: /var, /dev/stdout) | maillog_file_rotate_suffix (default: %Y%m%d-%H%M%S) | mailq_path (default: see postconf -d output) | manpage_directory (default: see postconf -d output) | maps_rbl_domains (default: empty) | maps_rbl_reject_code (default: 554) | masquerade_classes (default: envelope_sender, header_sender, header_recipient) | masquerade_domains (default: empty) | masquerade_exceptions (default: empty) | master_service_disable (default: empty) | max_idle (default: 100s) | max_use (default: 100) | maximal_backoff_time (default: 4000s) | maximal_queue_lifetime (default: 5d) | message_drop_headers (default: bcc, content-length, resent-bcc, return-path) | message_reject_characters (default: empty) | message_size_limit (default: 10240000) | message_strip_characters (default: empty) | meta_directory (default: see 'postconf -d' output) | milter_command_timeout (default: 30s) | milter_connect_macros (default: see postconf -d output) | milter_connect_timeout (default: 30s) | milter_content_timeout (default: 300s) | milter_data_macros (default: see postconf -d output) | milter_default_action (default: tempfail) | milter_end_of_data_macros (default: see postconf -d output) | milter_end_of_header_macros (default: see postconf -d output) | milter_header_checks (default: empty) | milter_helo_macros (default: see postconf -d output) | milter_macro_daemon_name (default: $myhostname) | milter_macro_defaults (default: empty) | milter_macro_v (default: $mail_name $mail_version) | milter_mail_macros (default: see postconf -d output) | milter_protocol (default: 6) | milter_rcpt_macros (default: see postconf -d output) | milter_unknown_command_macros (default: see postconf -d output) | mime_boundary_length_limit (default: 2048) | mime_header_checks (default: $header_checks) | mime_nesting_limit (default: 100) | minimal_backoff_time (default: 300s) | multi_instance_directories (default: empty) | multi_instance_enable (default: no) | multi_instance_group (default: empty) | multi_instance_name (default: empty) | multi_instance_wrapper (default: empty) | multi_recipient_bounce_reject_code (default: 550) | mydestination (default: $myhostname, localhost.$mydomain, localhost) | mydomain (default: see postconf -d output) | myhostname (default: see postconf -d output) | mynetworks (default: see postconf -d output) | mynetworks_style (default: Postfix >= 3.0: host, Postfix < 3.0: subnet) | myorigin (default: $myhostname) | nested_header_checks (default: $header_checks) | newaliases_path (default: see postconf -d output) | non_fqdn_reject_code (default: 504) | non_smtpd_milters (default: empty) | notify_classes (default: resource, software) | nullmx_reject_code (default: 556) | openssl_path (default: openssl) | owner_request_special (default: yes) | parent_domain_matches_subdomains (default: see postconf -d output) | permit_mx_backup_networks (default: empty) | pickup_service_name (default: pickup) | pipe_delivery_status_filter (default: $default_delivery_status_filter) | plaintext_reject_code (default: 450) | postlog_service_name (default: postlog) | postlogd_watchdog_timeout (default: 10s) | postmulti_control_commands (default: reload flush) | postmulti_start_commands (default: start) | postmulti_stop_commands (default: see postconf -d output) | postscreen_access_list (default: permit_mynetworks) | postscreen_bare_newline_action (default: ignore) | postscreen_bare_newline_enable (default: no) | postscreen_bare_newline_ttl (default: 30d) | postscreen_blacklist_action (default: ignore) | postscreen_cache_cleanup_interval (default: 12h) | postscreen_cache_map (default: btree:$data_directory/postscreen_cache) | postscreen_cache_retention_time (default: 7d) | postscreen_client_connection_count_limit (default: $smtpd_client_connec- | postscreen_command_count_limit (default: 20) | postscreen_command_filter (default: $smtpd_command_filter) | postscreen_command_time_limit (default: normal: 300s, overload: 10s) | postscreen_disable_vrfy_command (default: $disable_vrfy_command) | postscreen_discard_ehlo_keyword_address_maps (default: $smtpd_dis- | postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords) | postscreen_dnsbl_action (default: ignore) | postscreen_dnsbl_max_ttl (default: | postscreen_dnsbl_min_ttl (default: 60s) | postscreen_dnsbl_reply_map (default: empty) | postscreen_dnsbl_sites (default: empty) | postscreen_dnsbl_threshold (default: 1) | postscreen_dnsbl_timeout (default: 10s) | postscreen_dnsbl_ttl (default: 1h) | postscreen_dnsbl_whitelist_threshold (default: 0) | postscreen_enforce_tls (default: $smtpd_enforce_tls) | postscreen_expansion_filter (default: see postconf -d output) | postscreen_forbidden_commands (default: $smtpd_forbidden_commands) | postscreen_greet_action (default: ignore) | postscreen_greet_banner (default: $smtpd_banner) | postscreen_greet_ttl (default: 1d) | postscreen_greet_wait (default: normal: 6s, overload: 2s) | postscreen_helo_required (default: $smtpd_helo_required) | postscreen_non_smtp_command_action (default: drop) | postscreen_non_smtp_command_enable (default: no) | postscreen_non_smtp_command_ttl (default: 30d) | postscreen_pipelining_action (default: enforce) | postscreen_pipelining_enable (default: no) | postscreen_pipelining_ttl (default: 30d) | postscreen_post_queue_limit (default: $default_process_limit) | postscreen_pre_queue_limit (default: $default_process_limit) | postscreen_reject_footer (default: $smtpd_reject_footer) | postscreen_reject_footer_maps (default: $smtpd_reject_footer_maps) | postscreen_tls_security_level (default: $smtpd_tls_security_level) | postscreen_upstream_proxy_protocol (default: empty) | postscreen_upstream_proxy_timeout (default: 5s) | postscreen_use_tls (default: $smtpd_use_tls) | postscreen_watchdog_timeout (default: 10s) | postscreen_whitelist_interfaces (default: static:all) | prepend_delivered_header (default: command, file, forward) | process_id (read-only) | process_id_directory (default: pid) | process_name (read-only) | propagate_unmatched_extensions (default: canonical, virtual) | proxy_interfaces (default: empty) | proxy_read_maps (default: see postconf -d output) | proxy_write_maps (default: see postconf -d output) | proxymap_service_name (default: proxymap) | proxywrite_service_name (default: proxywrite) | qmgr_clog_warn_time (default: 300s) | qmgr_daemon_timeout (default: 1000s) | qmgr_fudge_factor (default: 100) | qmgr_ipc_timeout (default: 60s) | qmgr_message_active_limit (default: 20000) | qmgr_message_recipient_limit (default: 20000) | qmgr_message_recipient_minimum (default: 10) | qmqpd_authorized_clients (default: empty) | qmqpd_client_port_logging (default: no) | qmqpd_error_delay (default: 1s) | qmqpd_timeout (default: 300s) | queue_directory (default: see postconf -d output) | queue_file_attribute_count_limit (default: 100) | queue_minfree (default: 0) | queue_run_delay (default: 300s) | queue_service_name (default: qmgr) | rbl_reply_maps (default: empty) | readme_directory (default: see postconf -d output) | receive_override_options (default: empty) | recipient_bcc_maps (default: empty) | recipient_canonical_classes (default: envelope_recipient, header_recipient) | recipient_canonical_maps (default: empty) | recipient_delimiter (default: empty) | reject_code (default: 554) | reject_tempfail_action (default: defer_if_permit) | relay_clientcerts (default: empty) | relay_destination_concurrency_limit (default: $default_destination_concur- | relay_destination_recipient_limit (default: $default_destination_recipi- | relay_domains (default: Postfix >= 3.0: empty, Postfix < 3.0: $mydestination) | relay_domains_reject_code (default: 554) | relay_recipient_maps (default: empty) | relay_transport (default: relay) | relayhost (default: empty) | relocated_maps (default: empty) | remote_header_rewrite_domain (default: empty) | require_home_directory (default: no) | reset_owner_alias (default: no) | resolve_dequoted_address (default: yes) | resolve_null_domain (default: no) | resolve_numeric_domain (default: no) | rewrite_service_name (default: rewrite) | sample_directory (default: /etc/postfix) | send_cyrus_sasl_authzid (default: no) | sender_based_routing (default: no) | sender_bcc_maps (default: empty) | sender_canonical_classes (default: envelope_sender, header_sender) | sender_canonical_maps (default: empty) | sender_dependent_default_transport_maps (default: empty) | sender_dependent_relayhost_maps (default: empty) | sendmail_fix_line_endings (default: always) | sendmail_path (default: see postconf -d output) | service_name (read-only) | service_throttle_time (default: 60s) | setgid_group (default: postdrop) | shlib_directory (default: see 'postconf -d' output) | show_user_unknown_table_name (default: yes) | showq_service_name (default: showq) | smtp_address_preference (default: any) | smtp_address_verify_target (default: rcpt) | smtp_always_send_ehlo (default: yes) | smtp_balance_inet_protocols (default: yes) | smtp_bind_address (default: empty) | smtp_bind_address6 (default: empty) | smtp_body_checks (default: empty) | smtp_cname_overrides_servername (default: version dependent) | smtp_connect_timeout (default: 30s) | smtp_connection_cache_destinations (default: empty) | smtp_connection_cache_on_demand (default: yes) | smtp_connection_cache_time_limit (default: 2s) | smtp_connection_reuse_count_limit (default: 0) | smtp_connection_reuse_time_limit (default: 300s) | smtp_data_done_timeout (default: 600s) | smtp_data_init_timeout (default: 120s) | smtp_data_xfer_timeout (default: 180s) | smtp_defer_if_no_mx_address_found (default: no) | smtp_delivery_status_filter (default: $default_delivery_status_filter) | smtp_destination_concurrency_limit (default: $default_destination_concur- | smtp_destination_recipient_limit (default: $default_destination_recipi- | smtp_discard_ehlo_keyword_address_maps (default: empty) | smtp_discard_ehlo_keywords (default: empty) | smtp_dns_reply_filter (default: empty) | smtp_dns_resolver_options (default: empty) | smtp_dns_support_level (default: empty) | smtp_enforce_tls (default: no) | smtp_fallback_relay (default: $fallback_relay) | smtp_generic_maps (default: empty) | smtp_header_checks (default: empty) | smtp_helo_name (default: $myhostname) | smtp_helo_timeout (default: 300s) | smtp_host_lookup (default: dns) | smtp_line_length_limit (default: 998) | smtp_mail_timeout (default: 300s) | smtp_mime_header_checks (default: empty) | smtp_mx_address_limit (default: 5) | smtp_mx_session_limit (default: 2) | smtp_nested_header_checks (default: empty) | smtp_never_send_ehlo (default: no) | smtp_per_record_deadline (default: no) | smtp_pix_workaround_delay_time (default: 10s) | smtp_pix_workaround_maps (default: empty) | smtp_pix_workaround_threshold_time (default: 500s) | smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf) | smtp_quit_timeout (default: 300s) | smtp_quote_rfc821_envelope (default: yes) | smtp_randomize_addresses (default: yes) | smtp_rcpt_timeout (default: 300s) | smtp_reply_filter (default: empty) | smtp_rset_timeout (default: 20s) | smtp_sasl_auth_cache_name (default: empty) | smtp_sasl_auth_cache_time (default: 90d) | smtp_sasl_auth_enable (default: no) | smtp_sasl_auth_soft_bounce (default: yes) | smtp_sasl_mechanism_filter (default: empty) | smtp_sasl_password_maps (default: empty) | smtp_sasl_path (default: empty) | smtp_sasl_security_options (default: noplaintext, noanonymous) | smtp_sasl_tls_security_options (default: $smtp_sasl_security_options) | smtp_sasl_tls_verified_security_options (default: $smtp_sasl_tls_security_op- | smtp_sasl_type (default: cyrus) | smtp_send_dummy_mail_auth (default: no) | smtp_send_xforward_command (default: no) | smtp_sender_dependent_authentication (default: no) | smtp_skip_4xx_greeting (default: yes) | smtp_skip_5xx_greeting (default: yes) | smtp_skip_quit_response (default: yes) | smtp_starttls_timeout (default: 300s) | smtp_tcp_port (default: smtp) | smtp_tls_CAfile (default: empty) | smtp_tls_CApath (default: empty) | smtp_tls_block_early_mail_reply (default: no) | smtp_tls_cert_file (default: empty) | smtp_tls_chain_files (default: empty) | smtp_tls_cipherlist (default: empty) | smtp_tls_ciphers (default: medium) | smtp_tls_connection_reuse (default: no) | smtp_tls_dane_insecure_mx_policy (default: dane) | smtp_tls_dcert_file (default: empty) | smtp_tls_dkey_file (default: $smtp_tls_dcert_file) | smtp_tls_eccert_file (default: empty) | smtp_tls_eckey_file (default: $smtp_tls_eccert_file) | smtp_tls_enforce_peername (default: yes) | smtp_tls_exclude_ciphers (default: empty) | smtp_tls_fingerprint_cert_match (default: empty) | smtp_tls_fingerprint_digest (default: md5) | smtp_tls_force_insecure_host_tlsa_lookup (default: no) | smtp_tls_key_file (default: $smtp_tls_cert_file) | smtp_tls_loglevel (default: 0) | smtp_tls_mandatory_ciphers (default: medium) | smtp_tls_mandatory_exclude_ciphers (default: empty) | smtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3) | smtp_tls_note_starttls_offer (default: no) | smtp_tls_per_site (default: empty) | smtp_tls_policy_maps (default: empty) | smtp_tls_protocols (default: !SSLv2, !SSLv3) | smtp_tls_scert_verifydepth (default: 9) | smtp_tls_secure_cert_match (default: nexthop, dot-nexthop) | smtp_tls_security_level (default: empty) | smtp_tls_servername (default: empty) | smtp_tls_session_cache_database (default: empty) | smtp_tls_session_cache_timeout (default: 3600s) | smtp_tls_trust_anchor_file (default: empty) | smtp_tls_verify_cert_match (default: hostname) | smtp_tls_wrappermode (default: no) | smtp_use_tls (default: no) | smtp_xforward_timeout (default: 300s) | smtpd_authorized_verp_clients (default: $authorized_verp_clients) | smtpd_authorized_xclient_hosts (default: empty) | smtpd_authorized_xforward_hosts (default: empty) | smtpd_banner (default: $myhostname ESMTP $mail_name) | smtpd_client_auth_rate_limit (default: 0) | smtpd_client_connection_count_limit (default: 50) | smtpd_client_connection_rate_limit (default: 0) | smtpd_client_event_limit_exceptions (default: $mynetworks) | smtpd_client_message_rate_limit (default: 0) | smtpd_client_new_tls_session_rate_limit (default: 0) | smtpd_client_port_logging (default: no) | smtpd_client_recipient_rate_limit (default: 0) | smtpd_client_restrictions (default: empty) | smtpd_command_filter (default: empty) | smtpd_data_restrictions (default: empty) | smtpd_delay_open_until_valid_rcpt (default: yes) | smtpd_delay_reject (default: yes) | smtpd_discard_ehlo_keyword_address_maps (default: empty) | smtpd_discard_ehlo_keywords (default: empty) | smtpd_dns_reply_filter (default: empty) | smtpd_end_of_data_restrictions (default: empty) | smtpd_enforce_tls (default: no) | smtpd_error_sleep_time (default: 1s) | smtpd_etrn_restrictions (default: empty) | smtpd_expansion_filter (default: see postconf -d output) | smtpd_forbid_bare_newline (default: Postfix < 3.9: no) | smtpd_forbid_bare_newline_exclusions (default: $mynetworks) | smtpd_forbid_bare_newline_reject_code (default: 550) | smtpd_forbidden_commands (default: CONNECT, GET, POST) | smtpd_hard_error_limit (default: normal: 20, overload: 1) | smtpd_helo_required (default: no) | smtpd_helo_restrictions (default: empty) | smtpd_history_flush_threshold (default: 100) | smtpd_junk_command_limit (default: normal: 100, overload: 1) | smtpd_log_access_permit_actions (default: empty) | smtpd_milter_maps (default: empty) | smtpd_milters (default: empty) | smtpd_noop_commands (default: empty) | smtpd_null_access_lookup_key (default: <>) | smtpd_peername_lookup (default: yes) | smtpd_per_record_deadline (default: normal: no, overload: yes) | smtpd_policy_service_default_action (default: 451 4.3.5 Server configuration | smtpd_policy_service_max_idle (default: 300s) | smtpd_policy_service_max_ttl (default: 1000s) | smtpd_policy_service_policy_context (default: empty) | smtpd_policy_service_request_limit (default: 0) | smtpd_policy_service_retry_delay (default: 1s) | smtpd_policy_service_timeout (default: 100s) | smtpd_policy_service_try_limit (default: 2) | smtpd_proxy_ehlo (default: $myhostname) | smtpd_proxy_filter (default: empty) | smtpd_proxy_options (default: empty) | smtpd_proxy_timeout (default: 100s) | smtpd_recipient_limit (default: 1000) | smtpd_recipient_overshoot_limit (default: 1000) | smtpd_recipient_restrictions (default: see postconf -d output) | smtpd_reject_footer (default: empty) | smtpd_reject_footer_maps (default: empty) | smtpd_reject_unlisted_recipient (default: yes) | smtpd_reject_unlisted_sender (default: no) | smtpd_relay_restrictions (default: permit_mynetworks, permit_sasl_authenti- | smtpd_restriction_classes (default: empty) | smtpd_sasl_application_name (default: smtpd) | smtpd_sasl_auth_enable (default: no) | smtpd_sasl_authenticated_header (default: no) | smtpd_sasl_exceptions_networks (default: empty) | smtpd_sasl_local_domain (default: empty) | smtpd_sasl_path (default: smtpd) | smtpd_sasl_response_limit (default: 12288) | smtpd_sasl_security_options (default: noanonymous) | smtpd_sasl_service (default: smtp) | smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options) | smtpd_sasl_type (default: cyrus) | smtpd_sender_login_maps (default: empty) | smtpd_sender_restrictions (default: empty) | smtpd_service_name (default: smtpd) | smtpd_soft_error_limit (default: 10) | smtpd_starttls_timeout (default: see postconf -d output) | smtpd_timeout (default: normal: 300s, overload: 10s) | smtpd_tls_CAfile (default: empty) | smtpd_tls_CApath (default: empty) | smtpd_tls_always_issue_session_ids (default: yes) | smtpd_tls_ask_ccert (default: no) | smtpd_tls_auth_only (default: no) | smtpd_tls_ccert_verifydepth (default: 9) | smtpd_tls_cert_file (default: empty) | smtpd_tls_chain_files (default: empty) | smtpd_tls_cipherlist (default: empty) | smtpd_tls_ciphers (default: medium) | smtpd_tls_dcert_file (default: empty) | smtpd_tls_dh1024_param_file (default: empty) | smtpd_tls_dh512_param_file (default: empty) | smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file) | smtpd_tls_eccert_file (default: empty) | smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file) | smtpd_tls_eecdh_grade (default: see postconf -d output) | smtpd_tls_exclude_ciphers (default: empty) | smtpd_tls_fingerprint_digest (default: md5) | smtpd_tls_key_file (default: $smtpd_tls_cert_file) | smtpd_tls_loglevel (default: 0) | smtpd_tls_mandatory_ciphers (default: medium) | smtpd_tls_mandatory_exclude_ciphers (default: empty) | smtpd_tls_mandatory_protocols (default: !SSLv2, !SSLv3) | smtpd_tls_protocols (default: !SSLv2, !SSLv3) | smtpd_tls_received_header (default: no) | smtpd_tls_req_ccert (default: no) | smtpd_tls_security_level (default: empty) | smtpd_tls_session_cache_database (default: empty) | smtpd_tls_session_cache_timeout (default: 3600s) | smtpd_tls_wrappermode (default: no) | smtpd_upstream_proxy_protocol (default: empty) | smtpd_upstream_proxy_timeout (default: 5s) | smtpd_use_tls (default: no) | smtputf8_autodetect_classes (default: sendmail, verify) | smtputf8_enable (default: yes) | soft_bounce (default: no) | stale_lock_time (default: 500s) | stress (default: empty) | strict_7bit_headers (default: no) | strict_8bitmime (default: no) | strict_8bitmime_body (default: no) | strict_mailbox_ownership (default: yes) | strict_mime_encoding_domain (default: no) | strict_rfc821_envelopes (default: no) | strict_smtputf8 (default: no) | sun_mailtool_compatibility (default: no) | swap_bangpath (default: yes) | syslog_facility (default: mail) | syslog_name (default: see postconf -d output) | tcp_windowsize (default: 0) | tls_append_default_CA (default: no) | tls_daemon_random_bytes (default: 32) | tls_dane_digest_agility (default: on) | tls_dane_digests (default: sha512 sha256) | tls_dane_trust_anchor_digest_enable (default: yes) | tls_disable_workarounds (default: see postconf -d output) | tls_eecdh_auto_curves (default: see postconf -d output) | tls_eecdh_strong_curve (default: prime256v1) | tls_eecdh_ultra_curve (default: secp384r1) | tls_export_cipherlist (default: see postconf -d output) | tls_fast_shutdown_enable (default: yes) | tls_high_cipherlist (default: see postconf -d output) | tls_legacy_public_key_fingerprints (default: no) | tls_low_cipherlist (default: see postconf -d output) | tls_medium_cipherlist (default: see postconf -d output) | tls_null_cipherlist (default: eNULL:!aNULL) | tls_preempt_cipherlist (default: no) | tls_random_bytes (default: 32) | tls_random_exchange_name (default: see postconf -d output) | tls_random_prng_update_period (default: 3600s) | tls_random_reseed_period (default: 3600s) | tls_random_source (default: see postconf -d output) | tls_server_sni_maps (default: empty) | tls_ssl_options (default: empty) | tls_wildcard_matches_multiple_labels (default: yes) | tlsmgr_service_name (default: tlsmgr) | tlsproxy_client_CAfile (default: $smtp_tls_CAfile) | tlsproxy_client_CApath (default: $smtp_tls_CApath) | tlsproxy_client_cert_file (default: $smtp_tls_cert_file) | tlsproxy_client_chain_files (default: $smtp_tls_chain_files) | tlsproxy_client_dcert_file (default: $smtp_tls_dcert_file) | tlsproxy_client_dkey_file (default: $smtp_tls_dkey_file) | tlsproxy_client_eccert_file (default: $smtp_tls_eccert_file) | tlsproxy_client_eckey_file (default: $smtp_tls_eckey_file) | tlsproxy_client_enforce_tls (default: $smtp_enforce_tls) | tlsproxy_client_fingerprint_digest (default: $smtp_tls_fingerprint_digest) | tlsproxy_client_key_file (default: $smtp_tls_key_file) | tlsproxy_client_loglevel (default: $smtp_tls_loglevel) | tlsproxy_client_loglevel_parameter (default: smtp_tls_loglevel) | tlsproxy_client_per_site (default: $smtp_tls_per_site) | tlsproxy_client_policy_maps (default: $smtp_tls_policy_maps) | tlsproxy_client_scert_verifydepth (default: $smtp_tls_scert_verifydepth) | tlsproxy_client_security_level (default: $smtp_tls_security_level) | tlsproxy_client_use_tls (default: $smtp_use_tls) | tlsproxy_enforce_tls (default: $smtpd_enforce_tls) | tlsproxy_service_name (default: tlsproxy) | tlsproxy_tls_CAfile (default: $smtpd_tls_CAfile) | tlsproxy_tls_CApath (default: $smtpd_tls_CApath) | tlsproxy_tls_always_issue_session_ids (default: $smtpd_tls_always_issue_ses- | tlsproxy_tls_ask_ccert (default: $smtpd_tls_ask_ccert) | tlsproxy_tls_ccert_verifydepth (default: $smtpd_tls_ccert_verifydepth) | tlsproxy_tls_cert_file (default: $smtpd_tls_cert_file) | tlsproxy_tls_chain_files (default: $smtpd_tls_chain_files) | tlsproxy_tls_ciphers (default: $smtpd_tls_ciphers) | tlsproxy_tls_dcert_file (default: $smtpd_tls_dcert_file) | tlsproxy_tls_dh1024_param_file (default: $smtpd_tls_dh1024_param_file) | tlsproxy_tls_dh512_param_file (default: $smtpd_tls_dh512_param_file) | tlsproxy_tls_dkey_file (default: $smtpd_tls_dkey_file) | tlsproxy_tls_eccert_file (default: $smtpd_tls_eccert_file) | tlsproxy_tls_eckey_file (default: $smtpd_tls_eckey_file) | tlsproxy_tls_eecdh_grade (default: $smtpd_tls_eecdh_grade) | tlsproxy_tls_exclude_ciphers (default: $smtpd_tls_exclude_ciphers) | tlsproxy_tls_fingerprint_digest (default: $smtpd_tls_fingerprint_digest) | tlsproxy_tls_key_file (default: $smtpd_tls_key_file) | tlsproxy_tls_loglevel (default: $smtpd_tls_loglevel) | tlsproxy_tls_mandatory_ciphers (default: $smtpd_tls_mandatory_ciphers) | tlsproxy_tls_mandatory_exclude_ciphers (default: $smtpd_tls_mandatory_ex- | tlsproxy_tls_mandatory_protocols (default: $smtpd_tls_mandatory_protocols) | tlsproxy_tls_protocols (default: $smtpd_tls_protocols) | tlsproxy_tls_req_ccert (default: $smtpd_tls_req_ccert) | tlsproxy_tls_security_level (default: $smtpd_tls_security_level) | tlsproxy_tls_session_cache_timeout (default: $smtpd_tls_session_cache_timeout) | tlsproxy_use_tls (default: $smtpd_use_tls) | tlsproxy_watchdog_timeout (default: 10s) | trace_service_name (default: trace) | transport_delivery_slot_cost (default: $default_delivery_slot_cost) | transport_delivery_slot_discount (default: $default_delivery_slot_discount) | transport_delivery_slot_loan (default: $default_delivery_slot_loan) | transport_destination_concurrency_failed_cohort_limit (default: $default_des- | transport_destination_concurrency_limit (default: $default_destination_concur- | transport_destination_concurrency_negative_feedback (default: $default_desti- | transport_destination_concurrency_positive_feedback (default: $default_desti- | transport_destination_rate_delay (default: $default_destination_rate_delay) | transport_destination_recipient_limit (default: $default_destination_recipi- | transport_extra_recipient_limit (default: $default_extra_recipient_limit) | transport_initial_destination_concurrency (default: $initial_destination_con- | transport_maps (default: empty) | transport_minimum_delivery_slots (default: $default_minimum_delivery_slots) | transport_recipient_limit (default: $default_recipient_limit) | transport_recipient_refill_delay (default: $default_recipient_refill_delay) | transport_recipient_refill_limit (default: $default_recipient_refill_limit) | transport_retry_time (default: 60s) | transport_time_limit (default: $command_time_limit) | transport_transport_rate_delay (default: $default_transport_rate_delay) | trigger_timeout (default: 10s) | undisclosed_recipients_header (default: see postconf -d output) | unknown_address_reject_code (default: 450) | unknown_address_tempfail_action (default: $reject_tempfail_action) | unknown_client_reject_code (default: 450) | unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action) | unknown_hostname_reject_code (default: 450) | unknown_local_recipient_reject_code (default: 550) | unknown_relay_recipient_reject_code (default: 550) | unknown_virtual_alias_reject_code (default: 550) | unknown_virtual_mailbox_reject_code (default: 550) | unverified_recipient_defer_code (default: 450) | unverified_recipient_reject_code (default: 450) | unverified_recipient_reject_reason (default: empty) | unverified_recipient_tempfail_action (default: $reject_tempfail_action) | unverified_sender_defer_code (default: 450) | unverified_sender_reject_code (default: 450) | unverified_sender_reject_reason (default: empty) | unverified_sender_tempfail_action (default: $reject_tempfail_action) | verp_delimiter_filter (default: -=+) | virtual_alias_address_length_limit (default: 1000) | virtual_alias_domains (default: $virtual_alias_maps) | virtual_alias_expansion_limit (default: 1000) | virtual_alias_maps (default: $virtual_maps) | virtual_alias_recursion_limit (default: 1000) | virtual_delivery_status_filter (default: $default_delivery_status_filter) | virtual_destination_concurrency_limit (default: $default_destination_concur- | virtual_destination_recipient_limit (default: $default_destination_recipi- | virtual_gid_maps (default: empty) | virtual_mailbox_base (default: empty) | virtual_mailbox_domains (default: $virtual_mailbox_maps) | virtual_mailbox_limit (default: 51200000) | virtual_mailbox_lock (default: see postconf -d output) | virtual_mailbox_maps (default: empty) | virtual_maps (default: empty) | virtual_minimum_uid (default: 100) | virtual_transport (default: virtual) | virtual_uid_maps (default: empty) | SEE ALSO | LICENSE | AUTHOR(S)