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SMTP(8postfix)                                                  SMTP(8postfix)

NAME
       smtp - Postfix SMTP+LMTP client

SYNOPSIS
       smtp [generic Postfix daemon options]

DESCRIPTION
       The Postfix SMTP+LMTP client implements the SMTP and LMTP mail delivery
       protocols. It processes message delivery requests from the  queue  man-
       ager.  Each  request specifies a queue file, a sender address, a domain
       or host to deliver to, and recipient information.  This program expects
       to be run from the master(8) process manager.

       The  SMTP+LMTP  client  updates  the queue file and marks recipients as
       finished, or it informs the queue manager that delivery should be tried
       again  at  a  later  time.  Delivery  status  reports  are  sent to the
       bounce(8), defer(8) or trace(8) daemon as appropriate.

       The SMTP+LMTP client looks up a list of mail  exchanger  addresses  for
       the  destination  host,  sorts  the list by preference, and connects to
       each listed address until it finds a server that responds.

       When a server is not reachable, or when mail delivery fails  due  to  a
       recoverable  error  condition, the SMTP+LMTP client will try to deliver
       the mail to an alternate host.

       After a successful mail transaction, a connection may be saved  to  the
       scache(8)  connection  cache  server,  so  that  it  may be used by any
       SMTP+LMTP client for a subsequent transaction.

       By default, connection caching is enabled temporarily for  destinations
       that have a high volume of mail in the active queue. Connection caching
       can be enabled permanently for specific destinations.

SMTP DESTINATION SYNTAX
       SMTP destinations have the following form:

       domainname

       domainname:port
              Look up the mail exchangers for the specified domain,  and  con-
              nect to the specified port (default: smtp).

       [hostname]

       [hostname]:port
              Look  up  the  address(es) of the specified host, and connect to
              the specified port (default: smtp).

       [address]

       [address]:port
              Connect to the host at the specified address, and connect to the
              specified  port (default: smtp). An IPv6 address must be format-
              ted as [ipv6:address].

LMTP DESTINATION SYNTAX
       LMTP destinations have the following form:

       unix:pathname
              Connect to the local UNIX-domain server that  is  bound  to  the
              specified  pathname.  If  the process runs chrooted, an absolute
              pathname is interpreted relative to the Postfix queue directory.

       inet:hostname

       inet:hostname:port

       inet:[address]

       inet:[address]:port
              Connect to the specified TCP port on the specified local or  re-
              mote  host. If no port is specified, connect to the port defined
              as lmtp in services(4).   If  no  such  service  is  found,  the
              lmtp_tcp_port configuration parameter (default value of 24) will
              be used.  An IPv6 address must be formatted as [ipv6:address].

SECURITY
       The SMTP+LMTP client is moderately security-sensitive. It talks to SMTP
       or LMTP servers and to DNS servers on the network. The SMTP+LMTP client
       can be run chrooted at fixed low privilege.

STANDARDS
       RFC 821 (SMTP protocol)
       RFC 822 (ARPA Internet Text Messages)
       RFC 1651 (SMTP service extensions)
       RFC 1652 (8bit-MIME transport)
       RFC 1870 (Message Size Declaration)
       RFC 2033 (LMTP protocol)
       RFC 2034 (SMTP Enhanced Error Codes)
       RFC 2045 (MIME: Format of Internet Message Bodies)
       RFC 2046 (MIME: Media Types)
       RFC 2554 (AUTH command)
       RFC 2821 (SMTP protocol)
       RFC 2920 (SMTP Pipelining)
       RFC 3207 (STARTTLS command)
       RFC 3461 (SMTP DSN Extension)
       RFC 3463 (Enhanced Status Codes)
       RFC 4954 (AUTH command)
       RFC 5321 (SMTP protocol)
       RFC 6531 (Internationalized SMTP)
       RFC 6533 (Internationalized Delivery Status Notifications)
       RFC 7672 (SMTP security via opportunistic DANE TLS)

DIAGNOSTICS
       Problems and transactions are  logged  to  syslogd(8)  or  postlogd(8).
       Corrupted  message  files are marked so that the queue manager can move
       them to the corrupt queue for further inspection.

       Depending on the setting of the notify_classes parameter, the  postmas-
       ter is notified of bounces, protocol problems, and of other trouble.

BUGS
       SMTP  and  LMTP  connection  reuse for TLS (without closing the SMTP or
       LMTP connection) is not supported before Postfix 3.4.

       SMTP and LMTP connection caching  assumes  that  SASL  credentials  are
       valid  for  all  destinations that map onto the same IP address and TCP
       port.

CONFIGURATION PARAMETERS
       Before Postfix version 2.3, the LMTP client is a separate program  that
       implements  only  a  subset  of  the functionality available with SMTP:
       there is no support for TLS, and  connections  are  cached  in-process,
       making it ineffective when the client is used for multiple domains.

       Most smtp_xxx configuration parameters have an lmtp_xxx "mirror" param-
       eter for the equivalent LMTP  feature.  This  document  describes  only
       those LMTP-related parameters that aren't simply "mirror" parameters.

       Changes  to  main.cf  are picked up automatically, as smtp(8) processes
       run for only a limited amount of time. Use the command "postfix reload"
       to speed up a change.

       The  text  below provides only a parameter summary. See postconf(5) for
       more details including examples.

COMPATIBILITY CONTROLS
       ignore_mx_lookup_error (no)
              Ignore DNS MX lookups that produce no response.

       smtp_always_send_ehlo (yes)
              Always send EHLO at the start of an SMTP session.

       smtp_never_send_ehlo (no)
              Never send EHLO at the start of an SMTP session.

       smtp_defer_if_no_mx_address_found (no)
              Defer mail delivery when no MX record resolves to an IP address.

       smtp_line_length_limit (998)
              The maximal length of message header and body lines that Postfix
              will send via SMTP.

       smtp_pix_workaround_delay_time (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.

       smtp_pix_workaround_threshold_time (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.

       smtp_pix_workarounds (disable_esmtp, delay_dotcrlf)
              A  list  that  specifies  zero or more workarounds for CISCO PIX
              firewall bugs.

       smtp_pix_workaround_maps (empty)
              Lookup tables, indexed by the remote SMTP server  address,  with
              per-destination workarounds for CISCO PIX firewall bugs.

       smtp_quote_rfc821_envelope (yes)
              Quote  addresses  in  Postfix  SMTP client MAIL FROM and RCPT TO
              commands as required by RFC 5321.

       smtp_reply_filter (empty)
              A mechanism to transform replies from remote  SMTP  servers  one
              line at a time.

       smtp_skip_5xx_greeting (yes)
              Skip remote SMTP servers that greet with a 5XX status code.

       smtp_skip_quit_response (yes)
              Do not wait for the response to the SMTP QUIT command.

       Available in Postfix version 2.0 and earlier:

       smtp_skip_4xx_greeting (yes)
              Skip  SMTP  servers  that greet with a 4XX status code (go away,
              try again later).

       Available in Postfix version 2.2 and later:

       smtp_discard_ehlo_keyword_address_maps (empty)
              Lookup tables, indexed by the remote SMTP server  address,  with
              case  insensitive  lists of EHLO keywords (pipelining, starttls,
              auth, etc.) that the Postfix SMTP client will ignore in the EHLO
              response from a remote SMTP server.

       smtp_discard_ehlo_keywords (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.

       smtp_generic_maps (empty)
              Optional  lookup  tables  that  perform address rewriting in the
              Postfix SMTP client, typically to transform a locally valid  ad-
              dress into a globally valid address when sending mail across the
              Internet.

       Available in Postfix version 2.2.9 and later:

       smtp_cname_overrides_servername (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.

       Available in Postfix version 2.3 and later:

       lmtp_discard_lhlo_keyword_address_maps (empty)
              Lookup  tables,  indexed by the remote LMTP server address, with
              case insensitive lists of LHLO keywords  (pipelining,  starttls,
              auth, etc.) that the Postfix LMTP client will ignore in the LHLO
              response from a remote LMTP server.

       lmtp_discard_lhlo_keywords (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.

       Available in Postfix version 2.4.4 and later:

       send_cyrus_sasl_authzid (no)
              When authenticating to a remote SMTP or LMTP server with the de-
              fault  setting  "no",  send  no SASL authoriZation ID (authzid);
              send only the SASL authentiCation ID (authcid)  plus  the  auth-
              cid's password.

       Available in Postfix version 2.5 and later:

       smtp_header_checks (empty)
              Restricted header_checks(5) tables for the Postfix SMTP client.

       smtp_mime_header_checks (empty)
              Restricted  mime_header_checks(5)  tables  for  the Postfix SMTP
              client.

       smtp_nested_header_checks (empty)
              Restricted nested_header_checks(5) tables for the  Postfix  SMTP
              client.

       smtp_body_checks (empty)
              Restricted body_checks(5) tables for the Postfix SMTP client.

       Available in Postfix version 2.6 and later:

       tcp_windowsize (0)
              An  optional  workaround for routers that break TCP window scal-
              ing.

       Available in Postfix version 2.8 and later:

       smtp_dns_resolver_options (empty)
              DNS Resolver options for the Postfix SMTP client.

       Available in Postfix version 2.9 and later:

       smtp_per_record_deadline (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 message content line, or TLS protocol mes-
              sage).

       smtp_send_dummy_mail_auth (no)
              Whether or not to append the "AUTH=<>" option to the  MAIL  FROM
              command in SASL-authenticated SMTP sessions.

       Available in Postfix version 2.11 and later:

       smtp_dns_support_level (empty)
              Level of DNS support in the Postfix SMTP client.

       Available in Postfix version 3.0 and later:

       smtp_delivery_status_filter ($default_delivery_status_filter)
              Optional filter for the smtp(8) delivery agent to change the de-
              livery status code or explanatory text of successful  or  unsuc-
              cessful deliveries.

       smtp_dns_reply_filter (empty)
              Optional filter for Postfix SMTP client DNS lookup results.

       Available in Postfix version 3.3 and later:

       smtp_balance_inet_protocols (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.

MIME PROCESSING CONTROLS
       Available in Postfix version 2.0 and later:

       disable_mime_output_conversion (no)
              Disable the conversion of 8BITMIME format to 7BIT format.

       mime_boundary_length_limit (2048)
              The maximal length of MIME multipart boundary strings.

       mime_nesting_limit (100)
              The maximal recursion level that the MIME processor will handle.

EXTERNAL CONTENT INSPECTION CONTROLS
       Available in Postfix version 2.1 and later:

       smtp_send_xforward_command (no)
              Send  the  non-standard  XFORWARD  command when the Postfix SMTP
              server EHLO response announces XFORWARD support.

SASL AUTHENTICATION CONTROLS
       smtp_sasl_auth_enable (no)
              Enable SASL authentication in the Postfix SMTP client.

       smtp_sasl_password_maps (empty)
              Optional Postfix  SMTP  client  lookup  tables  with  one  user-
              name:password  entry per sender, remote hostname or next-hop do-
              main.

       smtp_sasl_security_options (noplaintext, noanonymous)
              Postfix SMTP client SASL security options; as of Postfix 2.3 the
              list  of available features depends on the SASL client implemen-
              tation that is selected with smtp_sasl_type.

       Available in Postfix version 2.2 and later:

       smtp_sasl_mechanism_filter (empty)
              If non-empty, a Postfix SMTP client filter for the  remote  SMTP
              server's list of offered SASL mechanisms.

       Available in Postfix version 2.3 and later:

       smtp_sender_dependent_authentication (no)
              Enable  sender-dependent  authentication  in  the  Postfix  SMTP
              client; this is available only  with  SASL  authentication,  and
              disables  SMTP  connection caching to ensure that mail from dif-
              ferent senders will use the appropriate credentials.

       smtp_sasl_path (empty)
              Implementation-specific information that the Postfix SMTP client
              passes  through  to  the SASL plug-in implementation that is se-
              lected with smtp_sasl_type.

       smtp_sasl_type (cyrus)
              The SASL plug-in type that the Postfix SMTP  client  should  use
              for authentication.

       Available in Postfix version 2.5 and later:

       smtp_sasl_auth_cache_name (empty)
              An  optional table to prevent repeated SASL authentication fail-
              ures with the same remote SMTP  server  hostname,  username  and
              password.

       smtp_sasl_auth_cache_time (90d)
              The  maximal age of an smtp_sasl_auth_cache_name entry before it
              is removed.

       smtp_sasl_auth_soft_bounce (yes)
              When a remote SMTP server rejects a SASL authentication  request
              with  a 535 reply code, defer mail delivery instead of returning
              mail as undeliverable.

       Available in Postfix version 2.9 and later:

       smtp_send_dummy_mail_auth (no)
              Whether or not to append the "AUTH=<>" option to the  MAIL  FROM
              command in SASL-authenticated SMTP sessions.

STARTTLS SUPPORT CONTROLS
       Detailed  information  about STARTTLS configuration may be found in the
       TLS_README document.

       smtp_tls_security_level (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_en-
              force_peername.

       smtp_sasl_tls_security_options ($smtp_sasl_security_options)
              The  SASL  authentication security options that the Postfix SMTP
              client uses for TLS encrypted SMTP sessions.

       smtp_starttls_timeout (300s)
              Time limit for Postfix SMTP client  write  and  read  operations
              during TLS startup and shutdown handshake procedures.

       smtp_tls_CAfile (empty)
              A  file  containing  CA certificates of root CAs trusted to sign
              either remote SMTP server certificates or intermediate  CA  cer-
              tificates.

       smtp_tls_CApath (empty)
              Directory  with  PEM format Certification Authority certificates
              that the Postfix SMTP client uses to verify a remote SMTP server
              certificate.

       smtp_tls_cert_file (empty)
              File with the Postfix SMTP client RSA certificate in PEM format.

       smtp_tls_mandatory_ciphers (medium)
              The  minimum  TLS cipher grade that the Postfix SMTP client will
              use with mandatory TLS encryption.

       smtp_tls_exclude_ciphers (empty)
              List of ciphers or cipher types to exclude from the Postfix SMTP
              client cipher list at all TLS security levels.

       smtp_tls_mandatory_exclude_ciphers (empty)
              Additional  list  of ciphers or cipher types to exclude from the
              Postfix SMTP client cipher list at mandatory TLS  security  lev-
              els.

       smtp_tls_dcert_file (empty)
              File with the Postfix SMTP client DSA certificate in PEM format.

       smtp_tls_dkey_file ($smtp_tls_dcert_file)
              File with the Postfix SMTP client DSA private key in PEM format.

       smtp_tls_key_file ($smtp_tls_cert_file)
              File with the Postfix SMTP client RSA private key in PEM format.

       smtp_tls_loglevel (0)
              Enable additional Postfix SMTP client logging of TLS activity.

       smtp_tls_note_starttls_offer (no)
              Log  the  hostname of a remote SMTP server that offers STARTTLS,
              when TLS is not already enabled for that server.

       smtp_tls_policy_maps (empty)
              Optional lookup tables with the Postfix SMTP client TLS security
              policy by next-hop destination; when a non-empty value is speci-
              fied, this overrides the obsolete smtp_tls_per_site parameter.

       smtp_tls_mandatory_protocols (!SSLv2, !SSLv3)
              List of SSL/TLS protocols that the Postfix SMTP client will  use
              with mandatory TLS encryption.

       smtp_tls_scert_verifydepth (9)
              The verification depth for remote SMTP server certificates.

       smtp_tls_secure_cert_match (nexthop, dot-nexthop)
              How  the  Postfix  SMTP  client  verifies the server certificate
              peername for the "secure" TLS security level.

       smtp_tls_session_cache_database (empty)
              Name of the file containing the optional Postfix SMTP client TLS
              session cache.

       smtp_tls_session_cache_timeout (3600s)
              The expiration time of Postfix SMTP client TLS session cache in-
              formation.

       smtp_tls_verify_cert_match (hostname)
              How the Postfix SMTP  client  verifies  the  server  certificate
              peername for the "verify" TLS security level.

       tls_daemon_random_bytes (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).

       tls_high_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "high" grade ciphers.

       tls_medium_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "medium" or higher grade ciphers.

       tls_low_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "low" or higher grade ciphers.

       tls_export_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "export" or higher grade ciphers.

       tls_null_cipherlist (eNULL:!aNULL)
              The OpenSSL cipherlist for "NULL" grade ciphers that provide au-
              thentication without encryption.

       Available in Postfix version 2.4 and later:

       smtp_sasl_tls_verified_security_options    ($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 certificate.

       Available in Postfix version 2.5 and later:

       smtp_tls_fingerprint_cert_match (empty)
              List  of  acceptable remote SMTP server certificate fingerprints
              for  the  "fingerprint"  TLS  security   level   (smtp_tls_secu-
              rity_level = fingerprint).

       smtp_tls_fingerprint_digest (md5)
              The  message  digest  algorithm  used  to  construct remote SMTP
              server certificate fingerprints.

       Available in Postfix version 2.6 and later:

       smtp_tls_protocols (!SSLv2, !SSLv3)
              List of TLS protocols that the Postfix SMTP client will  exclude
              or include with opportunistic TLS encryption.

       smtp_tls_ciphers (medium)
              The  minimum  TLS cipher grade that the Postfix SMTP client will
              use with opportunistic TLS encryption.

       smtp_tls_eccert_file (empty)
              File with the Postfix SMTP client ECDSA certificate in PEM  for-
              mat.

       smtp_tls_eckey_file ($smtp_tls_eccert_file)
              File  with the Postfix SMTP client ECDSA private key in PEM for-
              mat.

       Available in Postfix version 2.7 and later:

       smtp_tls_block_early_mail_reply (no)
              Try to detect a mail hijacking attack based on  a  TLS  protocol
              vulnerability  (CVE-2009-3555), where an attacker prepends mali-
              cious HELO, MAIL, RCPT, DATA commands to a Postfix  SMTP  client
              TLS session.

       Available in Postfix version 2.8 and later:

       tls_disable_workarounds (see 'postconf -d' output)
              List or bit-mask of OpenSSL bug work-arounds to disable.

       Available in Postfix version 2.11-3.1:

       tls_dane_digest_agility (on)
              Configure RFC7671 DANE TLSA digest algorithm agility.

       tls_dane_trust_anchor_digest_enable (yes)
              Enable support for RFC 6698 (DANE TLSA) DNS records that contain
              digests of trust-anchors with certificate usage "2".

       Available in Postfix version 2.11 and later:

       smtp_tls_trust_anchor_file (empty)
              Zero or more PEM-format  files  with  trust-anchor  certificates
              and/or public keys.

       smtp_tls_force_insecure_host_tlsa_lookup (no)
              Lookup  the  associated  DANE TLSA RRset even when a hostname is
              not an alias and its address records lie in an unsigned zone.

       tlsmgr_service_name (tlsmgr)
              The name of the tlsmgr(8) service entry in master.cf.

       Available in Postfix version 3.0 and later:

       smtp_tls_wrappermode (no)
              Request that the Postfix SMTP client connects using  the  legacy
              SMTPS protocol instead of using the STARTTLS command.

       Available in Postfix version 3.1 and later:

       smtp_tls_dane_insecure_mx_policy (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.

       Available in Postfix version 3.4 and later:

       smtp_tls_connection_reuse (no)
              Try to make multiple deliveries per TLS-encrypted connection.

       smtp_tls_chain_files (empty)
              List  of one or more PEM files, each holding one or more private
              keys directly followed by a corresponding certificate chain.

       smtp_tls_servername (empty)
              Optional name to send to the  remote  SMTP  server  in  the  TLS
              Server Name Indication (SNI) extension.

       Introduced with Postfix 3.4.6, 3.3.5, 3.2.10, and 3.1.13:

       tls_fast_shutdown_enable (yes)
              A workaround for implementations that hang Postfix while shuting
              down a TLS session, until Postfix times out.

OBSOLETE STARTTLS CONTROLS
       The following configuration parameters  exist  for  compatibility  with
       Postfix versions before 2.3. Support for these will be removed in a fu-
       ture release.

       smtp_use_tls (no)
              Opportunistic mode: use TLS when a remote SMTP server  announces
              STARTTLS support, otherwise send the mail in the clear.

       smtp_enforce_tls (no)
              Enforcement  mode:  require that remote SMTP servers use TLS en-
              cryption, and never send mail in the clear.

       smtp_tls_enforce_peername (yes)
              With mandatory TLS encryption,  require  that  the  remote  SMTP
              server  hostname  matches  the  information  in  the remote SMTP
              server certificate.

       smtp_tls_per_site (empty)
              Optional lookup tables with the Postfix SMTP  client  TLS  usage
              policy  by  next-hop destination and by remote SMTP server host-
              name.

       smtp_tls_cipherlist (empty)
              Obsolete Postfix < 2.3 control for the Postfix SMTP  client  TLS
              cipher list.

RESOURCE AND RATE CONTROLS
       smtp_connect_timeout (30s)
              The  Postfix SMTP client time limit for completing a TCP connec-
              tion, or zero (use the operating system built-in time limit).

       smtp_helo_timeout (300s)
              The Postfix SMTP client time limit for sending the HELO or  EHLO
              command,  and  for  receiving the initial remote SMTP server re-
              sponse.

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

       smtp_xforward_timeout (300s)
              The Postfix SMTP client time limit for sending the XFORWARD com-
              mand, and for receiving the remote SMTP server response.

       smtp_mail_timeout (300s)
              The Postfix SMTP client time limit for  sending  the  MAIL  FROM
              command, and for receiving the remote SMTP server response.

       smtp_rcpt_timeout (300s)
              The  Postfix SMTP client time limit for sending the SMTP RCPT TO
              command, and for receiving the remote SMTP server response.

       smtp_data_init_timeout (120s)
              The Postfix SMTP client time limit for  sending  the  SMTP  DATA
              command, and for receiving the remote SMTP server response.

       smtp_data_xfer_timeout (180s)
              The  Postfix SMTP client time limit for sending the SMTP message
              content.

       smtp_data_done_timeout (600s)
              The Postfix SMTP client time limit for sending the SMTP ".", and
              for receiving the remote SMTP server response.

       smtp_quit_timeout (300s)
              The Postfix SMTP client time limit for sending the QUIT command,
              and for receiving the remote SMTP server response.

       Available in Postfix version 2.1 and later:

       smtp_mx_address_limit (5)
              The maximal number of MX (mail exchanger) IP addresses that  can
              result  from Postfix SMTP client mail exchanger lookups, or zero
              (no limit).

       smtp_mx_session_limit (2)
              The maximal number of SMTP sessions per delivery request  before
              the  Postfix SMTP client gives up or delivers to a fall-back re-
              lay host, or zero (no limit).

       smtp_rset_timeout (20s)
              The Postfix SMTP client time limit for sending the RSET command,
              and for receiving the remote SMTP server response.

       Available in Postfix version 2.2 and earlier:

       lmtp_cache_connection (yes)
              Keep  Postfix  LMTP  client connections open for up to $max_idle
              seconds.

       Available in Postfix version 2.2 and later:

       smtp_connection_cache_destinations (empty)
              Permanently enable SMTP connection  caching  for  the  specified
              destinations.

       smtp_connection_cache_on_demand (yes)
              Temporarily  enable  SMTP connection caching while a destination
              has a high volume of mail in the active queue.

       smtp_connection_reuse_time_limit (300s)
              The amount of time during which Postfix will use an SMTP connec-
              tion repeatedly.

       smtp_connection_cache_time_limit (2s)
              When SMTP connection caching is enabled, the amount of time that
              an unused SMTP client socket is kept open before it is closed.

       Available in Postfix version 2.3 and later:

       connection_cache_protocol_timeout (5s)
              Time limit for connection cache connect, send or receive  opera-
              tions.

       Available in Postfix version 2.9 and later:

       smtp_per_record_deadline (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 message content line, or TLS  protocol  mes-
              sage).

       Available in Postfix version 2.11 and later:

       smtp_connection_reuse_count_limit (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).

       Available in Postfix version 3.4 and later:

       smtp_tls_connection_reuse (no)
              Try to make multiple deliveries per TLS-encrypted connection.

       Implemented in the qmgr(8) daemon:

       transport_destination_concurrency_limit   ($default_destination_concur-
       rency_limit)
              A transport-specific override for  the  default_destination_con-
              currency_limit parameter value, where transport is the master.cf
              name of the message delivery transport.

       transport_destination_recipient_limit     ($default_destination_recipi-
       ent_limit)
              A transport-specific override for the default_destination_recip-
              ient_limit parameter value, where  transport  is  the  master.cf
              name of the message delivery transport.

SMTPUTF8 CONTROLS
       Preliminary SMTPUTF8 support is introduced with Postfix 3.0.

       smtputf8_enable (yes)
              Enable  preliminary SMTPUTF8 support for the protocols described
              in RFC 6531..6533.

       smtputf8_autodetect_classes (sendmail, verify)
              Detect that a message requires SMTPUTF8 support for  the  speci-
              fied mail origin classes.

       Available in Postfix version 3.2 and later:

       enable_idna2003_compatibility (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.

TROUBLE SHOOTING CONTROLS
       debug_peer_level (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 (empty)
              Optional list of remote client or server hostname or network ad-
              dress  patterns that cause the verbose logging level to increase
              by the amount specified in $debug_peer_level.

       error_notice_recipient (postmaster)
              The recipient of postmaster notifications  about  mail  delivery
              problems that are caused by policy, resource, software or proto-
              col errors.

       internal_mail_filter_classes (empty)
              What categories of Postfix-generated mail  are  subject  to  be-
              fore-queue     content    inspection    by    non_smtpd_milters,
              header_checks and body_checks.

       notify_classes (resource, software)
              The list of error classes that are reported to the postmaster.

MISCELLANEOUS CONTROLS
       best_mx_transport (empty)
              Where the Postfix SMTP client should deliver mail  when  it  de-
              tects a "mail loops back to myself" error condition.

       config_directory (see 'postconf -d' output)
              The  default  location of the Postfix main.cf and master.cf con-
              figuration files.

       daemon_timeout (18000s)
              How much time a Postfix daemon process may take to handle a  re-
              quest before it is terminated by a built-in watchdog timer.

       delay_logging_resolution_limit (2)
              The  maximal  number of digits after the decimal point when log-
              ging sub-second delay values.

       disable_dns_lookups (no)
              Disable DNS lookups in the Postfix SMTP and LMTP clients.

       inet_interfaces (all)
              The network interface addresses that this mail  system  receives
              mail on.

       inet_protocols (all)
              The  Internet  protocols Postfix will attempt to use when making
              or accepting connections.

       ipc_timeout (3600s)
              The time limit for sending or receiving information over an  in-
              ternal communication channel.

       lmtp_assume_final (no)
              When  a remote LMTP server announces no DSN support, assume that
              the server performs final delivery, and send "delivered"  deliv-
              ery status notifications instead of "relayed".

       lmtp_tcp_port (24)
              The default TCP port that the Postfix LMTP client connects to.

       max_idle (100s)
              The  maximum  amount of time that an idle Postfix daemon process
              waits for an incoming connection before terminating voluntarily.

       max_use (100)
              The maximal number of incoming connections that a Postfix daemon
              process will service before terminating voluntarily.

       process_id (read-only)
              The process ID of a Postfix command or daemon process.

       process_name (read-only)
              The process name of a Postfix command or daemon process.

       proxy_interfaces (empty)
              The  network  interface addresses that this mail system receives
              mail on by way of a proxy or network address translation unit.

       smtp_address_preference (any)
              The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP
              client  will try first, when a destination has IPv6 and IPv4 ad-
              dresses with equal MX preference.

       smtp_bind_address (empty)
              An optional numerical network  address  that  the  Postfix  SMTP
              client should bind to when making an IPv4 connection.

       smtp_bind_address6 (empty)
              An  optional  numerical  network  address  that the Postfix SMTP
              client should bind to when making an IPv6 connection.

       smtp_helo_name ($myhostname)
              The hostname to send in the SMTP HELO or EHLO command.

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

       smtp_host_lookup (dns)
              What mechanisms the Postfix SMTP client uses to look up a host's
              IP address.

       smtp_randomize_addresses (yes)
              Randomize the order of equal-preference MX host addresses.

       syslog_facility (mail)
              The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
              A  prefix  that  is  prepended  to  the  process  name in syslog
              records, so that, for example, "smtpd" becomes "prefix/smtpd".

       Available with Postfix 2.2 and earlier:

       fallback_relay (empty)
              Optional list of relay hosts for SMTP destinations that can't be
              found or that are unreachable.

       Available with Postfix 2.3 and later:

       smtp_fallback_relay ($fallback_relay)
              Optional list of relay hosts for SMTP destinations that can't be
              found or that are unreachable.

       Available with Postfix 3.0 and later:

       smtp_address_verify_target (rcpt)
              In the context of email address verification, the SMTP  protocol
              stage that determines whether an email address is deliverable.

       Available with Postfix 3.1 and later:

       lmtp_fallback_relay (empty)
              Optional list of relay hosts for LMTP destinations that can't be
              found or that are unreachable.

       Available with Postfix 3.2 and later:

       smtp_tcp_port (smtp)
              The default TCP port that the Postfix SMTP client connects to.

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

SEE ALSO
       generic(5), output address rewriting
       header_checks(5), message header content inspection
       body_checks(5), body parts content inspection
       qmgr(8), queue manager
       bounce(8), delivery status reports
       scache(8), connection cache server
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       tlsmgr(8), TLS session and PRNG management
       postlogd(8), Postfix logging
       syslogd(8), system logging

README FILES
       Use "postconf readme_directory" or "postconf html_directory" to  locate
       this information.
       SASL_README, Postfix SASL howto
       TLS_README, Postfix STARTTLS howto

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

       Command pipelining in cooperation with:
       Jon Ribbens
       Oaktree Internet Solutions Ltd.,
       Internet House,
       Canal Basin,
       Coventry,
       CV1 4LY, United Kingdom.

       SASL support originally by:
       Till Franke
       SuSE Rhein/Main AG
       65760 Eschborn, Germany

       TLS support originally by:
       Lutz Jaenicke
       BTU Cottbus
       Allgemeine Elektrotechnik
       Universitaetsplatz 3-4
       D-03044 Cottbus, Germany

       Revised TLS and SMTP connection cache support by:
       Victor Duchovni
       Morgan Stanley

                                                                SMTP(8postfix)

NAME | SYNOPSIS | DESCRIPTION | SMTP DESTINATION SYNTAX | LMTP DESTINATION SYNTAX | SECURITY | STANDARDS | DIAGNOSTICS | BUGS | CONFIGURATION PARAMETERS | COMPATIBILITY CONTROLS | MIME PROCESSING CONTROLS | EXTERNAL CONTENT INSPECTION CONTROLS | SASL AUTHENTICATION CONTROLS | STARTTLS SUPPORT CONTROLS | OBSOLETE STARTTLS CONTROLS | RESOURCE AND RATE CONTROLS | SMTPUTF8 CONTROLS | TROUBLE SHOOTING CONTROLS | MISCELLANEOUS CONTROLS | SEE ALSO | README FILES | LICENSE | AUTHOR(S)