1QMGR(8)                     System Manager's Manual                    QMGR(8)
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NAME

6       qmgr - Postfix queue manager
7

SYNOPSIS

9       qmgr [generic Postfix daemon options]
10

DESCRIPTION

12       The qmgr(8) daemon awaits the arrival of incoming mail and arranges for
13       its delivery via Postfix delivery processes.  The actual  mail  routing
14       strategy  is  delegated to the trivial-rewrite(8) daemon.  This program
15       expects to be run from the master(8) process manager.
16
17       Mail addressed to the local double-bounce address is  logged  and  dis‐
18       carded.   This  stops  potential  loops  caused by undeliverable bounce
19       notifications.
20

MAIL QUEUES

22       The qmgr(8) daemon maintains the following queues:
23
24       incoming
25              Inbound mail from the network, or mail picked up  by  the  local
26              pickup(8) daemon from the maildrop directory.
27
28       active Messages  that the queue manager has opened for delivery. Only a
29              limited number of messages is allowed to enter the active  queue
30              (leaky bucket strategy, for a fixed delivery rate).
31
32       deferred
33              Mail  that  could  not  be delivered upon the first attempt. The
34              queue manager implements exponential  backoff  by  doubling  the
35              time between delivery attempts.
36
37       corrupt
38              Unreadable or damaged queue files are moved here for inspection.
39
40       hold   Messages  that  are  kept  "on hold" are kept here until someone
41              sets them free.
42

DELIVERY STATUS REPORTS

44       The qmgr(8) daemon keeps an eye on per-message delivery status  reports
45       in the following directories. Each status report file has the same name
46       as the corresponding message file:
47
48       bounce Per-recipient status information  about  why  mail  is  bounced.
49              These files are maintained by the bounce(8) daemon.
50
51       defer  Per-recipient  status  information  about  why  mail is delayed.
52              These files are maintained by the defer(8) daemon.
53
54       trace  Per-recipient status information as requested with  the  Postfix
55              "sendmail  -v" or "sendmail -bv" command.  These files are main‐
56              tained by the trace(8) daemon.
57
58       The qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or
59       trace(8) daemons to send delivery reports.
60

STRATEGIES

62       The queue manager implements a variety of strategies for either opening
63       queue files (input) or for message delivery (output).
64
65       leaky bucket
66              This strategy limits the number of messages in the active  queue
67              and  prevents the queue manager from running out of memory under
68              heavy load.
69
70       fairness
71              When the active queue has room, the queue manager takes one mes‐
72              sage  from  the  incoming queue and one from the deferred queue.
73              This prevents a large mail backlog from blocking the delivery of
74              new mail.
75
76       slow start
77              This  strategy  eliminates  "thundering herd" problems by slowly
78              adjusting the number of parallel deliveries to the same destina‐
79              tion.
80
81       round robin
82              The  queue  manager  sorts  delivery  requests  by  destination.
83              Round-robin selection prevents one destination  from  dominating
84              deliveries to other destinations.
85
86       exponential backoff
87              Mail  that  cannot  be  delivered  upon  the  first  attempt  is
88              deferred.  The time interval between delivery attempts  is  dou‐
89              bled after each attempt.
90
91       destination status cache
92              The  queue manager avoids unnecessary delivery attempts by main‐
93              taining a short-term, in-memory  list  of  unreachable  destina‐
94              tions.
95
96       preemptive message scheduling
97              The queue manager attempts to minimize the average per-recipient
98              delay while still preserving  the  correct  per-message  delays,
99              using a sophisticated preemptive message scheduling.
100

TRIGGERS

102       On  an  idle system, the queue manager waits for the arrival of trigger
103       events, or it waits for a timer to go off. A trigger is a one-byte mes‐
104       sage.   Depending  on  the message received, the queue manager performs
105       one of the following actions (the message is followed by  the  symbolic
106       constant used internally by the software):
107
108       D (QMGR_REQ_SCAN_DEFERRED)
109              Start  a  deferred  queue  scan.   If  a  deferred queue scan is
110              already in progress, that scan will be restarted as soon  as  it
111              finishes.
112
113       I (QMGR_REQ_SCAN_INCOMING)
114              Start  an  incoming  queue  scan.  If  an incoming queue scan is
115              already in progress, that scan will be restarted as soon  as  it
116              finishes.
117
118       A (QMGR_REQ_SCAN_ALL)
119              Ignore  deferred queue file time stamps. The request affects the
120              next deferred queue scan.
121
122       F (QMGR_REQ_FLUSH_DEAD)
123              Purge all information about dead transports and destinations.
124
125       W (TRIGGER_REQ_WAKEUP)
126              Wakeup call, This is used by the master  server  to  instantiate
127              servers  that should not go away forever. The action is to start
128              an incoming queue scan.
129
130       The qmgr(8) daemon reads an entire buffer worth of triggers.   Multiple
131       identical trigger requests are collapsed into one, and trigger requests
132       are sorted so that A and F precede D and I. Thus, in order to  force  a
133       deferred  queue  run,  one  would request A F D; in order to notify the
134       queue manager of the arrival of new mail one would request I.
135

STANDARDS

137       RFC 3463 (Enhanced status codes)
138       RFC 3464 (Delivery status notifications)
139

SECURITY

141       The qmgr(8) daemon is not security sensitive. It reads single-character
142       messages  from  untrusted  local  users, and thus may be susceptible to
143       denial of service attacks. The qmgr(8) daemon does not talk to the out‐
144       side  world,  and  it  can  be run at fixed low privilege in a chrooted
145       environment.
146

DIAGNOSTICS

148       Problems and transactions are  logged  to  syslogd(8)  or  postlogd(8).
149       Corrupted  message  files  are  saved  to the corrupt queue for further
150       inspection.
151
152       Depending on the setting of the notify_classes parameter, the  postmas‐
153       ter is notified of bounces and of other trouble.
154

BUGS

156       A single queue manager process has to compete for disk access with mul‐
157       tiple front-end processes such as cleanup(8). A sudden burst of inbound
158       mail can negatively impact outbound delivery rates.
159

CONFIGURATION PARAMETERS

161       Changes to main.cf are not picked up automatically as qmgr(8) is a per‐
162       sistent process. Use the "postfix reload" command after a configuration
163       change.
164
165       The  text  below provides only a parameter summary. See postconf(5) for
166       more details including examples.
167
168       In the text below, transport is the first field in a master.cf entry.
169

COMPATIBILITY CONTROLS

171       Available before Postfix version 2.5:
172
173       allow_min_user (no)
174              Allow a sender or recipient address to have  `-'  as  the  first
175              character.
176
177       Available with Postfix version 2.7 and later:
178
179       default_filter_nexthop (empty)
180              When  a  content_filter  or FILTER request specifies no explicit
181              next-hop destination, use $default_filter_nexthop instead;  when
182              that value is empty, use the domain in the recipient address.
183

ACTIVE QUEUE CONTROLS

185       qmgr_clog_warn_time (300s)
186              The  minimal  delay between warnings that a specific destination
187              is clogging up the Postfix active queue.
188
189       qmgr_message_active_limit (20000)
190              The maximal number of messages in the active queue.
191
192       qmgr_message_recipient_limit (20000)
193              The maximal number of recipients held in memory by  the  Postfix
194              queue manager, and the maximal size of the short-term, in-memory
195              "dead" destination status cache.
196
197       qmgr_message_recipient_minimum (10)
198              The minimal number of in-memory recipients for any message.
199
200       default_recipient_limit (20000)
201              The default per-transport upper limit on the number of in-memory
202              recipients.
203
204       transport_recipient_limit ($default_recipient_limit)
205              A  transport-specific  override  for the default_recipient_limit
206              parameter value, where transport is the master.cf  name  of  the
207              message delivery transport.
208
209       default_extra_recipient_limit (1000)
210              The  default  value for the extra per-transport limit imposed on
211              the number of in-memory recipients.
212
213       transport_extra_recipient_limit ($default_extra_recipient_limit)
214              A  transport-specific  override  for  the  default_extra_recipi‐
215              ent_limit parameter value, where transport is the master.cf name
216              of the message delivery transport.
217
218       Available in Postfix version 2.4 and later:
219
220       default_recipient_refill_limit (100)
221              The default per-transport limit  on  the  number  of  recipients
222              refilled at once.
223
224       transport_recipient_refill_limit ($default_recipient_refill_limit)
225              A    transport-specific   override   for   the   default_recipi‐
226              ent_refill_limit parameter value, where transport  is  the  mas‐
227              ter.cf name of the message delivery transport.
228
229       default_recipient_refill_delay (5s)
230              The  default  per-transport  maximum  delay  between  recipients
231              refills.
232
233       transport_recipient_refill_delay ($default_recipient_refill_delay)
234              A   transport-specific   override   for   the    default_recipi‐
235              ent_refill_delay  parameter  value,  where transport is the mas‐
236              ter.cf name of the message delivery transport.
237

DELIVERY CONCURRENCY CONTROLS

239       initial_destination_concurrency (5)
240              The  initial  per-destination  concurrency  level  for  parallel
241              delivery to the same destination.
242
243       default_destination_concurrency_limit (20)
244              The  default  maximal  number of parallel deliveries to the same
245              destination.
246
247       transport_destination_concurrency_limit   ($default_destination_concur‐
248       rency_limit)
249              A  transport-specific  override for the default_destination_con‐
250              currency_limit parameter value, where transport is the master.cf
251              name of the message delivery transport.
252
253       Available in Postfix version 2.5 and later:
254
255       transport_initial_destination_concurrency ($initial_destination_concur‐
256       rency)
257              A transport-specific override for  the  initial_destination_con‐
258              currency  parameter value, where transport is the master.cf name
259              of the message delivery transport.
260
261       default_destination_concurrency_failed_cohort_limit (1)
262              How many pseudo-cohorts  must  suffer  connection  or  handshake
263              failure  before a specific destination is considered unavailable
264              (and further delivery is suspended).
265
266       transport_destination_concurrency_failed_cohort_limit  ($default_desti‐
267       nation_concurrency_failed_cohort_limit)
268              A  transport-specific  override for the default_destination_con‐
269              currency_failed_cohort_limit parameter value, where transport is
270              the master.cf name of the message delivery transport.
271
272       default_destination_concurrency_negative_feedback (1)
273              The  per-destination  amount  of  delivery  concurrency negative
274              feedback, after a delivery completes with a connection or  hand‐
275              shake failure.
276
277       transport_destination_concurrency_negative_feedback  ($default_destina‐
278       tion_concurrency_negative_feedback)
279              A transport-specific override for  the  default_destination_con‐
280              currency_negative_feedback  parameter  value, where transport is
281              the master.cf name of the message delivery transport.
282
283       default_destination_concurrency_positive_feedback (1)
284              The per-destination  amount  of  delivery  concurrency  positive
285              feedback, after a delivery completes without connection or hand‐
286              shake failure.
287
288       transport_destination_concurrency_positive_feedback  ($default_destina‐
289       tion_concurrency_positive_feedback)
290              A  transport-specific  override for the default_destination_con‐
291              currency_positive_feedback parameter value, where  transport  is
292              the master.cf name of the message delivery transport.
293
294       destination_concurrency_feedback_debug (no)
295              Make  the queue manager's feedback algorithm verbose for perfor‐
296              mance analysis purposes.
297

RECIPIENT SCHEDULING CONTROLS

299       default_destination_recipient_limit (50)
300              The default maximal number of recipients per message delivery.
301
302       transport_destination_recipient_limit     ($default_destination_recipi‐
303       ent_limit)
304              A transport-specific override for the default_destination_recip‐
305              ient_limit parameter value, where  transport  is  the  master.cf
306              name of the message delivery transport.
307

MESSAGE SCHEDULING CONTROLS

309       default_delivery_slot_cost (5)
310              How  often  the  Postfix queue manager's scheduler is allowed to
311              preempt delivery of one message with another.
312
313       transport_delivery_slot_cost ($default_delivery_slot_cost)
314              A transport-specific override for the default_delivery_slot_cost
315              parameter  value,  where  transport is the master.cf name of the
316              message delivery transport.
317
318       default_minimum_delivery_slots (3)
319              How many recipients a message must have in order to  invoke  the
320              Postfix queue manager's scheduling algorithm at all.
321
322       transport_minimum_delivery_slots ($default_minimum_delivery_slots)
323              A  transport-specific  override  for  the default_minimum_deliv‐
324              ery_slots parameter value, where transport is the master.cf name
325              of the message delivery transport.
326
327       default_delivery_slot_discount (50)
328              The default value for transport-specific _delivery_slot_discount
329              settings.
330
331       transport_delivery_slot_discount ($default_delivery_slot_discount)
332              A transport-specific override for the default_delivery_slot_dis‐
333              count  parameter value, where transport is the master.cf name of
334              the message delivery transport.
335
336       default_delivery_slot_loan (3)
337              The default  value  for  transport-specific  _delivery_slot_loan
338              settings.
339
340       transport_delivery_slot_loan ($default_delivery_slot_loan)
341              A transport-specific override for the default_delivery_slot_loan
342              parameter value, where transport is the master.cf  name  of  the
343              message delivery transport.
344

OTHER RESOURCE AND RATE CONTROLS

346       minimal_backoff_time (300s)
347              The minimal time between attempts to deliver a deferred message;
348              prior to Postfix 2.4 the default value was 1000s.
349
350       maximal_backoff_time (4000s)
351              The maximal time between attempts to deliver a deferred message.
352
353       maximal_queue_lifetime (5d)
354              Consider a message as undeliverable, when delivery fails with  a
355              temporary error, and the time in the queue has reached the maxi‐
356              mal_queue_lifetime limit.
357
358       queue_run_delay (300s)
359              The time between deferred queue  scans  by  the  queue  manager;
360              prior to Postfix 2.4 the default value was 1000s.
361
362       transport_retry_time (60s)
363              The  time  between attempts by the Postfix queue manager to con‐
364              tact a malfunctioning message delivery transport.
365
366       Available in Postfix version 2.1 and later:
367
368       bounce_queue_lifetime (5d)
369              Consider a bounce message as undeliverable, when delivery  fails
370              with  a  temporary  error, and the time in the queue has reached
371              the bounce_queue_lifetime limit.
372
373       Available in Postfix version 2.5 and later:
374
375       default_destination_rate_delay (0s)
376              The default amount of delay that is inserted between  individual
377              message  deliveries  to  the  same destination and over the same
378              message delivery transport.
379
380       transport_destination_rate_delay ($default_destination_rate_delay)
381              A   transport-specific   override   for   the   default_destina‐
382              tion_rate_delay  parameter  value,  where  transport is the mas‐
383              ter.cf name of the message delivery transport.
384
385       Available in Postfix version 3.1 and later:
386
387       default_transport_rate_delay (0s)
388              The default amount of delay that is inserted between  individual
389              message  deliveries  over  the  same message delivery transport,
390              regardless of destination.
391
392       transport_transport_rate_delay ($default_transport_rate_delay)
393              A   transport-specific   override   for    the    default_trans‐
394              port_rate_delay  parameter value, where the initial transport in
395              the parameter name is the master.cf name of the message delivery
396              transport.
397

SAFETY CONTROLS

399       qmgr_daemon_timeout (1000s)
400              How much time a Postfix queue manager process may take to handle
401              a request before it is terminated by a built-in watchdog timer.
402
403       qmgr_ipc_timeout (60s)
404              The time limit for the queue manager to send or receive informa‐
405              tion over an internal communication channel.
406
407       Available in Postfix version 3.1 and later:
408
409       address_verify_pending_request_limit (see 'postconf -d' output)
410              A  safety limit that prevents address verification requests from
411              overwhelming the Postfix queue.
412

MISCELLANEOUS CONTROLS

414       config_directory (see 'postconf -d' output)
415              The default location of the Postfix main.cf and  master.cf  con‐
416              figuration files.
417
418       defer_transports (empty)
419              The names of message delivery transports that should not deliver
420              mail unless someone issues "sendmail -q" or equivalent.
421
422       delay_logging_resolution_limit (2)
423              The maximal number of digits after the decimal point  when  log‐
424              ging sub-second delay values.
425
426       helpful_warnings (yes)
427              Log  warnings about problematic configuration settings, and pro‐
428              vide helpful suggestions.
429
430       process_id (read-only)
431              The process ID of a Postfix command or daemon process.
432
433       process_name (read-only)
434              The process name of a Postfix command or daemon process.
435
436       queue_directory (see 'postconf -d' output)
437              The location of the Postfix top-level queue directory.
438
439       syslog_facility (mail)
440              The syslog facility of Postfix logging.
441
442       syslog_name (see 'postconf -d' output)
443              A prefix that  is  prepended  to  the  process  name  in  syslog
444              records, so that, for example, "smtpd" becomes "prefix/smtpd".
445
446       Available in Postfix version 3.0 and later:
447
448       confirm_delay_cleared (no)
449              After  sending  a "your message is delayed" notification, inform
450              the sender when the delay clears up.
451
452       Available in Postfix 3.3 and later:
453
454       service_name (read-only)
455              The master.cf service name of a Postfix daemon process.
456

FILES

458       /var/spool/postfix/incoming, incoming queue
459       /var/spool/postfix/active, active queue
460       /var/spool/postfix/deferred, deferred queue
461       /var/spool/postfix/bounce, non-delivery status
462       /var/spool/postfix/defer, non-delivery status
463       /var/spool/postfix/trace, delivery status
464

SEE ALSO

466       trivial-rewrite(8), address routing
467       bounce(8), delivery status reports
468       postconf(5), configuration parameters
469       master(5), generic daemon options
470       master(8), process manager
471       postlogd(8), Postfix logging
472       syslogd(8), system logging
473

README FILES

475       Use "postconf readme_directory" or "postconf html_directory" to  locate
476       this information.
477       SCHEDULER_README, scheduling algorithm
478       QSHAPE_README, Postfix queue analysis
479

LICENSE

481       The Secure Mailer license must be distributed with this software.
482

AUTHOR(S)

484       Wietse Venema
485       IBM T.J. Watson Research
486       P.O. Box 704
487       Yorktown Heights, NY 10598, USA
488
489       Preemptive scheduler enhancements:
490       Patrik Rak
491       Modra 6
492       155 00, Prague, Czech Republic
493
494       Wietse Venema
495       Google, Inc.
496       111 8th Avenue
497       New York, NY 10011, USA
498
499
500
501                                                                       QMGR(8)
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