QMGR(8)                                                   QMGR(8)

NAME
       qmgr - Postfix queue manager

SYNOPSIS
       qmgr [generic Postfix daemon options]

DESCRIPTION
       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 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 daemon maintains the following queues:

       incoming
              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).

       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 daemon keeps an eye on per-message delivery sta-
       tus 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  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 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 pre-
       cede 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
       None. The qmgr daemon does not interact with  the  outside
       world.

SECURITY
       The  qmgr  daemon is not security sensitive. It reads sin-
       gle-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 environment.

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 smtpd.  A
       sudden  burst  of  inbound mail can negatively impact out-
       bound delivery rates.

CONFIGURATION PARAMETERS
       Changes to main.cf are  not  picked  up  automatically  as
       qmgr(8)  processes  are persistent. 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 be delivered to  unless  someone  issues
              "sendmail -q" or equivalent.

       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 pro-
              cess.

       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  pro-
              cess  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(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)