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QMGR(8postfix)                                                  QMGR(8postfix)

NAME
       qmgr - Postfix queue manager

SYNOPSIS
       qmgr [generic Postfix daemon options]

DESCRIPTION
       The qmgr(8) daemon awaits the arrival of incoming mail and arranges for
       its delivery via Postfix delivery processes.  The actual  mail  routing
       strategy  is  delegated to the trivial-rewrite(8) daemon.  This program
       expects to be run from the master(8) process manager.

       Mail addressed to the local double-bounce address is  logged  and  dis-
       carded.   This stops potential loops caused by undeliverable bounce no-
       tifications.

MAIL QUEUES
       The qmgr(8) daemon maintains the following queues:

       incoming
              Inbound mail from the network, or mail picked up  by  the  local
              pickup(8) daemon from the maildrop directory.

       active Messages  that the queue manager has opened for delivery. Only a
              limited number of messages is allowed to enter the active  queue
              (leaky bucket strategy, for a fixed delivery rate).

       deferred
              Mail  that  could  not  be delivered upon the first attempt. The
              queue manager implements exponential  backoff  by  doubling  the
              time between delivery attempts.

       corrupt
              Unreadable or damaged queue files are moved here for inspection.

       hold   Messages  that  are  kept  "on hold" are kept here until someone
              sets them free.

DELIVERY STATUS REPORTS
       The qmgr(8) daemon keeps an eye on per-message delivery status  reports
       in the following directories. Each status report file has the same name
       as the corresponding message file:

       bounce Per-recipient status information  about  why  mail  is  bounced.
              These files are maintained by the bounce(8) daemon.

       defer  Per-recipient  status  information  about  why  mail is delayed.
              These files are maintained by the defer(8) daemon.

       trace  Per-recipient status information as requested with  the  Postfix
              "sendmail  -v" or "sendmail -bv" command.  These files are main-
              tained by the trace(8) daemon.

       The qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or
       trace(8) daemons to send delivery reports.

STRATEGIES
       The queue manager implements a variety of strategies for either opening
       queue files (input) or for message delivery (output).

       leaky bucket
              This strategy limits the number of messages in the active  queue
              and  prevents the queue manager from running out of memory under
              heavy load.

       fairness
              When the active queue has room, the queue manager takes one mes-
              sage  from  the  incoming queue and one from the deferred queue.
              This prevents a large mail backlog from blocking the delivery of
              new mail.

       slow start
              This  strategy  eliminates  "thundering herd" problems by slowly
              adjusting the number of parallel deliveries to the same destina-
              tion.

       round robin
              The  queue  manager  sorts  delivery  requests  by  destination.
              Round-robin selection prevents one destination  from  dominating
              deliveries to other destinations.

       exponential backoff
              Mail  that  cannot  be  delivered  upon the first attempt is de-
              ferred.  The time interval between delivery attempts is  doubled
              after each attempt.

       destination status cache
              The  queue manager avoids unnecessary delivery attempts by main-
              taining a short-term, in-memory  list  of  unreachable  destina-
              tions.

       preemptive message scheduling
              The queue manager attempts to minimize the average per-recipient
              delay while still preserving the correct per-message delays, us-
              ing a sophisticated preemptive message scheduling.

TRIGGERS
       On  an  idle system, the queue manager waits for the arrival of trigger
       events, or it waits for a timer to go off. A trigger is a one-byte mes-
       sage.   Depending  on  the message received, the queue manager performs
       one of the following actions (the message is followed by  the  symbolic
       constant used internally by the software):

       D (QMGR_REQ_SCAN_DEFERRED)
              Start  a  deferred  queue scan.  If a deferred queue scan is al-
              ready in progress, that scan will be restarted  as  soon  as  it
              finishes.

       I (QMGR_REQ_SCAN_INCOMING)
              Start  an  incoming queue scan. If an incoming queue scan is al-
              ready in progress, that scan will be restarted  as  soon  as  it
              finishes.

       A (QMGR_REQ_SCAN_ALL)
              Ignore  deferred queue file time stamps. The request affects the
              next deferred queue scan.

       F (QMGR_REQ_FLUSH_DEAD)
              Purge all information about dead transports and destinations.

       W (TRIGGER_REQ_WAKEUP)
              Wakeup call, This is used by the master  server  to  instantiate
              servers  that should not go away forever. The action is to start
              an incoming queue scan.

       The qmgr(8) daemon reads an entire buffer worth of triggers.   Multiple
       identical trigger requests are collapsed into one, and trigger requests
       are sorted so that A and F precede D and I. Thus, in order to  force  a
       deferred  queue  run,  one  would request A F D; in order to notify the
       queue manager of the arrival of new mail one would request I.

STANDARDS
       RFC 3463 (Enhanced status codes)
       RFC 3464 (Delivery status notifications)

SECURITY
       The qmgr(8) daemon is not security sensitive. It reads single-character
       messages from untrusted local users, and thus may be susceptible to de-
       nial of service attacks. The qmgr(8) daemon does not talk to  the  out-
       side  world, and it can be run at fixed low privilege in a chrooted en-
       vironment.

DIAGNOSTICS
       Problems and transactions are  logged  to  syslogd(8)  or  postlogd(8).
       Corrupted  message files are saved to the corrupt queue for further in-
       spection.

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

BUGS
       A single queue manager process has to compete for disk access with mul-
       tiple front-end processes such as cleanup(8). A sudden burst of inbound
       mail can negatively impact outbound delivery rates.

CONFIGURATION PARAMETERS
       Changes to main.cf are not picked up automatically as qmgr(8) is a per-
       sistent process. Use the "postfix reload" command after a configuration
       change.

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

       In the text below, transport is the first field in a master.cf entry.

COMPATIBILITY CONTROLS
       Available before Postfix version 2.5:

       allow_min_user (no)
              Allow a sender or recipient address to have  `-'  as  the  first
              character.

       Available with Postfix version 2.7 and later:

       default_filter_nexthop (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.

ACTIVE QUEUE CONTROLS
       qmgr_clog_warn_time (300s)
              The  minimal  delay between warnings that a specific destination
              is clogging up the Postfix active queue.

       qmgr_message_active_limit (20000)
              The maximal number of messages in the active queue.

       qmgr_message_recipient_limit (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" destination status cache.

       qmgr_message_recipient_minimum (10)
              The minimal number of in-memory recipients for any message.

       default_recipient_limit (20000)
              The default per-transport upper limit on the number of in-memory
              recipients.

       transport_recipient_limit ($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.

       default_extra_recipient_limit (1000)
              The  default  value for the extra per-transport limit imposed on
              the number of in-memory recipients.

       transport_extra_recipient_limit ($default_extra_recipient_limit)
              A  transport-specific  override  for  the  default_extra_recipi-
              ent_limit parameter value, where transport is the master.cf name
              of the message delivery transport.

       Available in Postfix version 2.4 and later:

       default_recipient_refill_limit (100)
              The default per-transport limit on the number of recipients  re-
              filled at once.

       transport_recipient_refill_limit ($default_recipient_refill_limit)
              A  transport-specific  override  for  the  default_recipient_re-
              fill_limit parameter value, where  transport  is  the  master.cf
              name of the message delivery transport.

       default_recipient_refill_delay (5s)
              The  default  per-transport maximum delay between recipients re-
              fills.

       transport_recipient_refill_delay ($default_recipient_refill_delay)
              A  transport-specific  override  for  the  default_recipient_re-
              fill_delay  parameter  value,  where  transport is the master.cf
              name of the message delivery transport.

DELIVERY CONCURRENCY CONTROLS
       initial_destination_concurrency (5)
              The initial per-destination concurrency level for  parallel  de-
              livery to the same destination.

       default_destination_concurrency_limit (20)
              The  default  maximal  number of parallel deliveries to the same
              destination.

       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.

       Available in Postfix version 2.5 and later:

       transport_initial_destination_concurrency ($initial_destination_concur-
       rency)
              A transport-specific override for  the  initial_destination_con-
              currency  parameter value, where transport is the master.cf name
              of the message delivery transport.

       default_destination_concurrency_failed_cohort_limit (1)
              How many pseudo-cohorts  must  suffer  connection  or  handshake
              failure  before a specific destination is considered unavailable
              (and further delivery is suspended).

       transport_destination_concurrency_failed_cohort_limit  ($default_desti-
       nation_concurrency_failed_cohort_limit)
              A  transport-specific  override for the default_destination_con-
              currency_failed_cohort_limit parameter value, where transport is
              the master.cf name of the message delivery transport.

       default_destination_concurrency_negative_feedback (1)
              The  per-destination  amount  of  delivery  concurrency negative
              feedback, after a delivery completes with a connection or  hand-
              shake failure.

       transport_destination_concurrency_negative_feedback  ($default_destina-
       tion_concurrency_negative_feedback)
              A transport-specific override for  the  default_destination_con-
              currency_negative_feedback  parameter  value, where transport is
              the master.cf name of the message delivery transport.

       default_destination_concurrency_positive_feedback (1)
              The per-destination  amount  of  delivery  concurrency  positive
              feedback, after a delivery completes without connection or hand-
              shake failure.

       transport_destination_concurrency_positive_feedback  ($default_destina-
       tion_concurrency_positive_feedback)
              A  transport-specific  override for the default_destination_con-
              currency_positive_feedback parameter value, where  transport  is
              the master.cf name of the message delivery transport.

       destination_concurrency_feedback_debug (no)
              Make  the queue manager's feedback algorithm verbose for perfor-
              mance analysis purposes.

RECIPIENT SCHEDULING CONTROLS
       default_destination_recipient_limit (50)
              The default maximal number of recipients per message delivery.

       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.

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

       transport_delivery_slot_cost ($default_delivery_slot_cost)
              A transport-specific override for the default_delivery_slot_cost
              parameter  value,  where  transport is the master.cf name of the
              message delivery transport.

       default_minimum_delivery_slots (3)
              How many recipients a message must have in order to  invoke  the
              Postfix queue manager's scheduling algorithm at all.

       transport_minimum_delivery_slots ($default_minimum_delivery_slots)
              A  transport-specific  override  for  the default_minimum_deliv-
              ery_slots parameter value, where transport is the master.cf name
              of the message delivery transport.

       default_delivery_slot_discount (50)
              The default value for transport-specific _delivery_slot_discount
              settings.

       transport_delivery_slot_discount ($default_delivery_slot_discount)
              A transport-specific override for the default_delivery_slot_dis-
              count  parameter value, where transport is the master.cf name of
              the message delivery transport.

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

       transport_delivery_slot_loan ($default_delivery_slot_loan)
              A transport-specific override for the default_delivery_slot_loan
              parameter value, where transport is the master.cf  name  of  the
              message delivery transport.

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

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

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

       queue_run_delay (300s)
              The time between deferred queue  scans  by  the  queue  manager;
              prior to Postfix 2.4 the default value was 1000s.

       transport_retry_time (60s)
              The  time  between attempts by the Postfix queue manager to con-
              tact a malfunctioning message delivery transport.

       Available in Postfix version 2.1 and later:

       bounce_queue_lifetime (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.

       Available in Postfix version 2.5 and later:

       default_destination_rate_delay (0s)
              The default amount of delay that is inserted between  individual
              message  deliveries  to  the  same destination and over the same
              message delivery transport.

       transport_destination_rate_delay ($default_destination_rate_delay)
              A   transport-specific   override   for   the   default_destina-
              tion_rate_delay  parameter  value,  where  transport is the mas-
              ter.cf name of the message delivery transport.

       Available in Postfix version 3.1 and later:

       default_transport_rate_delay (0s)
              The default amount of delay that is inserted between  individual
              message deliveries over the same message delivery transport, re-
              gardless of destination.

       transport_transport_rate_delay ($default_transport_rate_delay)
              A transport-specific override for the default_transport_rate_de-
              lay  parameter value, where the initial transport in the parame-
              ter name is the master.cf name of the  message  delivery  trans-
              port.

SAFETY CONTROLS
       qmgr_daemon_timeout (1000s)
              How much time a Postfix queue manager process may take to handle
              a request before it is terminated by a built-in watchdog timer.

       qmgr_ipc_timeout (60s)
              The time limit for the queue manager to send or receive informa-
              tion over an internal communication channel.

       Available in Postfix version 3.1 and later:

       address_verify_pending_request_limit (see 'postconf -d' output)
              A  safety limit that prevents address verification requests from
              overwhelming the Postfix queue.

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

       defer_transports (empty)
              The names of message delivery transports that should not deliver
              mail unless someone issues "sendmail -q" or equivalent.

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

       helpful_warnings (yes)
              Log  warnings about problematic configuration settings, and pro-
              vide helpful suggestions.

       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.

       queue_directory (see 'postconf -d' output)
              The location of the Postfix top-level queue directory.

       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 in Postfix version 3.0 and later:

       confirm_delay_cleared (no)
              After  sending  a "your message is delayed" notification, inform
              the sender when the delay clears up.

       Available in Postfix 3.3 and later:

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

FILES
       /var/spool/postfix/incoming, incoming queue
       /var/spool/postfix/active, active queue
       /var/spool/postfix/deferred, deferred queue
       /var/spool/postfix/bounce, non-delivery status
       /var/spool/postfix/defer, non-delivery status
       /var/spool/postfix/trace, delivery status

SEE ALSO
       trivial-rewrite(8), address routing
       bounce(8), delivery status reports
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       postlogd(8), Postfix logging
       syslogd(8), system logging

README FILES
       Use "postconf readme_directory" or "postconf html_directory" to  locate
       this information.
       SCHEDULER_README, scheduling algorithm
       QSHAPE_README, Postfix queue analysis

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

       Preemptive scheduler enhancements:
       Patrik Rak
       Modra 6
       155 00, Prague, Czech Republic

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

                                                                QMGR(8postfix)

NAME | SYNOPSIS | DESCRIPTION | MAIL QUEUES | DELIVERY STATUS REPORTS | STRATEGIES | TRIGGERS | STANDARDS | SECURITY | DIAGNOSTICS | BUGS | CONFIGURATION PARAMETERS | COMPATIBILITY CONTROLS | ACTIVE QUEUE CONTROLS | DELIVERY CONCURRENCY CONTROLS | RECIPIENT SCHEDULING CONTROLS | MESSAGE SCHEDULING CONTROLS | OTHER RESOURCE AND RATE CONTROLS | SAFETY CONTROLS | MISCELLANEOUS CONTROLS | FILES | SEE ALSO | README FILES | LICENSE | AUTHOR(S)