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QMGR(8)                                                                QMGR(8)

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 triv-
       ial-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 discarded.  This stops potential  loops  caused
       by undeliverable bounce notifications.

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 direc-
              tory.

       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" com-
              mand.  These files are maintained 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 message 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 deliver-
              ies to the same destination.

       round robin
              The queue manager sorts delivery requests by desti-
              nation.   Round-robin selection prevents one desti-
              nation from dominating deliveries to other destina-
              tions.

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

       destination status cache
              The   queue  manager  avoids  unnecessary  delivery
              attempts by  maintaining  a  short-term,  in-memory
              list of unreachable destinations.

       preemptive message scheduling
              The  queue manager attempts to minimize the average
              per-recipient delay while still preserving the cor-
              rect per-message delays, using a sophisticated pre-
              emptive 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 message.  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 already 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 already 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  for-
              ever.  The  action  is  to  start an incoming queue
              scan.

       The qmgr(8) daemon reads an entire buffer worth  of  trig-
       gers.   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 denial of service attacks. The
       qmgr(8) daemon does not talk to the outside world, and  it
       can  be  run at fixed low privilege in a chrooted environ-
       ment.

DIAGNOSTICS
       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  postmaster  is notified of bounces and of other trou-
       ble.

BUGS
       A single queue manager process has  to  compete  for  disk
       access   with   multiple   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 persistent 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  mas-
       ter.cf entry.

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

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 size of the short-term, in-memory "dead" desti-
              nation 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 recipients.

       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_recipi-
       ent_limit)
              Idem, for delivery via the named message transport.

DELIVERY CONCURRENCY CONTROLS
       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 destination.

       transport_destination_concurrency_limit ($default_destina-
       tion_concurrency_limit)
              Idem, for delivery via the named message transport.

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

       transport_destination_recipient_limit   ($default_destina-
       tion_recipient_limit)
              Idem, for delivery via the named message 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)
              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 algo-
              rithm at all.

       transport_minimum_delivery_slots  ($default_minimum_deliv-
       ery_slots)
              Idem, for delivery via the named message transport.

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

       transport_delivery_slot_discount          ($default_deliv-
       ery_slot_discount)
              Idem, for delivery via the named message transport.

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

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

OTHER RESOURCE AND RATE CONTROLS
       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 undeliverable.

       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 man-
              ager  to  contact 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 considered undeliverable.

MISCELLANEOUS CONTROLS
       config_directory (see 'postconf -d' output)
              The  default  location  of  the Postfix main.cf and
              master.cf configuration 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  deliver  mail  unless  someone  issues
              "sendmail -q" or equivalent.

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

       helpful_warnings (yes)
              Log  warnings  about problematic configuration set-
              tings, and provide 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 direc-
              tory.

       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, "postfix/smtpd".

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
       syslogd(8), system logging

README FILES
       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

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

                                                                       QMGR(8)