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QMGR(8)                     System Manager's Manual                    QMGR(8)

       qmgr - Postfix queue manager

       qmgr [generic Postfix daemon options]

       The  qmgr  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

       The qmgr daemon maintains the following queues:

              Inbound mail from the network, or mail picked up  by  the  local
              pickup agent 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).

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

              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.

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

       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.

              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-

       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
              deferred.  The time interval between delivery attempts  is  dou-
              bled 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-

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

       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):

              Start  a  deferred  queue  scan.   If  a  deferred queue scan is
              already in progress, that scan will be restarted as soon  as  it

              Start  an  incoming  queue  scan.  If  an incoming queue scan is
              already in progress, that scan will be restarted as soon  as  it

              Ignore  deferred queue file time stamps. The request affects the
              next deferred queue scan.

              Purge all information about dead transports and destinations.

              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 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.

       None. The qmgr daemon does not interact with the outside world.

       The qmgr daemon is not security sensitive.  It  reads  single-character
       messages  from  untrusted  local  users, and thus may be susceptible to
       denial of service attacks. The qmgr daemon does not talk to the outside
       world,  and it can be run at fixed low privilege in a chrooted environ-

       Problems and transactions are logged to the syslog  daemon.   Corrupted
       message files are saved to the corrupt queue for further inspection.

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

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

       Changes to main.cf are not picked up automatically as qmgr(8) processes
       are  persistent.  Use  the postfix reload command after a configuration

       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.

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

       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 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 (10000)
              The default per-transport upper limit on the number of in-memory

       transport_recipient_limit ($default_recipient_limit)
              Idem, for delivery via the named message 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)
              Idem, for delivery via the named message transport.

       initial_destination_concurrency (5)
              The  initial  per-destination  concurrency  level  for  parallel
              delivery to the same destination.

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

       transport_destination_concurrency_limit   ($default_destination_concur-
              Idem, for delivery via the named message transport.

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

       transport_destination_recipient_limit     ($default_destination_recipi-
              Idem, for delivery via the named message transport.

       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)
              Idem, for delivery via the named message 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)
              Idem, for delivery via the named message transport.

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

       transport_delivery_slot_discount ($default_delivery_slot_discount)
              Idem, for delivery via the named message transport.

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

       transport_delivery_slot_loan ($default_delivery_slot_loan)
              Idem, for delivery via the named message transport.

       minimal_backoff_time (1000s)
              The minimal time between attempts to deliver a deferred message.

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

       maximal_queue_lifetime (5d)
              The maximal time a message is queued before it is sent  back  as

       queue_run_delay (1000s)
              The time between deferred queue scans by the queue manager.

       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)
              The maximal time a bounce message is queued before it is consid-
              ered undeliverable.

       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
              request before it is terminated by a built-in watchdog timer.

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

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

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

       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 (postfix)
              The mail system name that is prepended to the  process  name  in
              syslog  records,  so  that  "smtpd" becomes, for example, "post-

       /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

       trivial-rewrite(8), address routing
       bounce(8), delivery status reports
       postconf(5), configuration parameters
       master(8), process manager
       syslogd(8) system logging

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

       The Secure Mailer license must be distributed with this software.

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

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