    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)