1QMGR(8) System Manager's Manual QMGR(8)
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6 qmgr - Postfix queue manager
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9 qmgr [generic Postfix daemon options]
10
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 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
22 The qmgr(8) daemon maintains the following queues:
23 incoming
25 Inbound mail from the network, or mail picked up by the local
26 pickup(8) daemon from the maildrop directory.
27 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 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 corrupt
38 Unreadable or damaged queue files are moved here for inspection.
39 hold Messages that are kept "on hold" are kept here until someone
41 sets them free.
42
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 bounce Per-recipient status information about why mail is bounced.
49 These files are maintained by the bounce(8) daemon.
50 defer Per-recipient status information about why mail is delayed.
52 These files are maintained by the defer(8) daemon.
53 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 The qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or
59 trace(8) daemons to send delivery reports.
60
62 The queue manager implements a variety of strategies for either opening
63 queue files (input) or for message delivery (output).
64 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 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 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 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 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 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 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
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 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 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 A (QMGR_REQ_SCAN_ALL)
119 Ignore deferred queue file time stamps. The request affects the
120 next deferred queue scan.
121 F (QMGR_REQ_FLUSH_DEAD)
123 Purge all information about dead transports and destinations.
124 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 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
137 RFC 3463 (Enhanced status codes)
138 RFC 3464 (Delivery status notifications)
139
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
148 Problems and transactions are logged to the syslog daemon. Corrupted
149 message files are saved to the corrupt queue for further inspection.
150 Depending on the setting of the notify_classes parameter, the postmas‐
152 ter is notified of bounces and of other trouble.
153
155 A single queue manager process has to compete for disk access with mul‐
156 tiple front-end processes such as cleanup(8). A sudden burst of inbound
157 mail can negatively impact outbound delivery rates.
158
160 Changes to main.cf are not picked up automatically as qmgr(8) is a per‐
161 sistent process. Use the "postfix reload" command after a configuration
162 change.
163 The text below provides only a parameter summary. See postconf(5) for
165 more details including examples.
166 In the text below, transport is the first field in a master.cf entry.
168
170 Available before Postfix version 2.5:
171 allow_min_user (no)
173 Allow a sender or recipient address to have `-' as the first
174 character.
175 Available with Postfix version 2.7 and later:
177 default_filter_nexthop (empty)
179 When a content_filter or FILTER request specifies no explicit
180 next-hop destination, use $default_filter_nexthop instead; when
181 that value is empty, use the domain in the recipient address.
182
184 qmgr_clog_warn_time (300s)
185 The minimal delay between warnings that a specific destination
186 is clogging up the Postfix active queue.
187 qmgr_message_active_limit (20000)
189 The maximal number of messages in the active queue.
190 qmgr_message_recipient_limit (20000)
192 The maximal number of recipients held in memory by the Postfix
193 queue manager, and the maximal size of the short-term, in-memory
194 "dead" destination status cache.
195 qmgr_message_recipient_minimum (10)
197 The minimal number of in-memory recipients for any message.
198 default_recipient_limit (20000)
200 The default per-transport upper limit on the number of in-memory
201 recipients.
202 transport_recipient_limit ($default_recipient_limit)
204 A transport-specific override for the default_recipient_limit
205 parameter value, where transport is the master.cf name of the
206 message delivery transport.
207 default_extra_recipient_limit (1000)
209 The default value for the extra per-transport limit imposed on
210 the number of in-memory recipients.
211 transport_extra_recipient_limit ($default_extra_recipient_limit)
213 A transport-specific override for the default_extra_recipi‐
214 ent_limit parameter value, where transport is the master.cf name
215 of the message delivery transport.
216 Available in Postfix version 2.4 and later:
218 default_recipient_refill_limit (100)
220 The default per-transport limit on the number of recipients
221 refilled at once.
222 transport_recipient_refill_limit ($default_recipient_refill_limit)
224 A transport-specific override for the default_recipi‐
225 ent_refill_limit parameter value, where transport is the mas‐
226 ter.cf name of the message delivery transport.
227 default_recipient_refill_delay (5s)
229 The default per-transport maximum delay between recipients
230 refills.
231 transport_recipient_refill_delay ($default_recipient_refill_delay)
233 A transport-specific override for the default_recipi‐
234 ent_refill_delay parameter value, where transport is the mas‐
235 ter.cf name of the message delivery transport.
236
238 initial_destination_concurrency (5)
239 The initial per-destination concurrency level for parallel
240 delivery to the same destination.
241 default_destination_concurrency_limit (20)
243 The default maximal number of parallel deliveries to the same
244 destination.
245 transport_destination_concurrency_limit ($default_destination_concur‐
247 rency_limit)
248 A transport-specific override for the default_destination_con‐
249 currency_limit parameter value, where transport is the master.cf
250 name of the message delivery transport.
251 Available in Postfix version 2.5 and later:
253 transport_initial_destination_concurrency ($initial_destination_concur‐
255 rency)
256 A transport-specific override for the initial_destination_con‐
257 currency parameter value, where transport is the master.cf name
258 of the message delivery transport.
259 default_destination_concurrency_failed_cohort_limit (1)
261 How many pseudo-cohorts must suffer connection or handshake
262 failure before a specific destination is considered unavailable
263 (and further delivery is suspended).
264 transport_destination_concurrency_failed_cohort_limit ($default_desti‐
266 nation_concurrency_failed_cohort_limit)
267 A transport-specific override for the default_destination_con‐
268 currency_failed_cohort_limit parameter value, where transport is
269 the master.cf name of the message delivery transport.
270 default_destination_concurrency_negative_feedback (1)
272 The per-destination amount of delivery concurrency negative
273 feedback, after a delivery completes with a connection or hand‐
274 shake failure.
275 transport_destination_concurrency_negative_feedback ($default_destina‐
277 tion_concurrency_negative_feedback)
278 A transport-specific override for the default_destination_con‐
279 currency_negative_feedback parameter value, where transport is
280 the master.cf name of the message delivery transport.
281 default_destination_concurrency_positive_feedback (1)
283 The per-destination amount of delivery concurrency positive
284 feedback, after a delivery completes without connection or hand‐
285 shake failure.
286 transport_destination_concurrency_positive_feedback ($default_destina‐
288 tion_concurrency_positive_feedback)
289 A transport-specific override for the default_destination_con‐
290 currency_positive_feedback parameter value, where transport is
291 the master.cf name of the message delivery transport.
292 destination_concurrency_feedback_debug (no)
294 Make the queue manager's feedback algorithm verbose for perfor‐
295 mance analysis purposes.
296
298 default_destination_recipient_limit (50)
299 The default maximal number of recipients per message delivery.
300 transport_destination_recipient_limit ($default_destination_recipi‐
302 ent_limit)
303 A transport-specific override for the default_destination_recip‐
304 ient_limit parameter value, where transport is the master.cf
305 name of the message delivery transport.
306
308 default_delivery_slot_cost (5)
309 How often the Postfix queue manager's scheduler is allowed to
310 preempt delivery of one message with another.
311 transport_delivery_slot_cost ($default_delivery_slot_cost)
313 A transport-specific override for the default_delivery_slot_cost
314 parameter value, where transport is the master.cf name of the
315 message delivery transport.
316 default_minimum_delivery_slots (3)
318 How many recipients a message must have in order to invoke the
319 Postfix queue manager's scheduling algorithm at all.
320 transport_minimum_delivery_slots ($default_minimum_delivery_slots)
322 A transport-specific override for the default_minimum_deliv‐
323 ery_slots parameter value, where transport is the master.cf name
324 of the message delivery transport.
325 default_delivery_slot_discount (50)
327 The default value for transport-specific _delivery_slot_discount
328 settings.
329 transport_delivery_slot_discount ($default_delivery_slot_discount)
331 A transport-specific override for the default_delivery_slot_dis‐
332 count parameter value, where transport is the master.cf name of
333 the message delivery transport.
334 default_delivery_slot_loan (3)
336 The default value for transport-specific _delivery_slot_loan
337 settings.
338 transport_delivery_slot_loan ($default_delivery_slot_loan)
340 A transport-specific override for the default_delivery_slot_loan
341 parameter value, where transport is the master.cf name of the
342 message delivery transport.
343
345 minimal_backoff_time (300s)
346 The minimal time between attempts to deliver a deferred message;
347 prior to Postfix 2.4 the default value was 1000s.
348 maximal_backoff_time (4000s)
350 The maximal time between attempts to deliver a deferred message.
351 maximal_queue_lifetime (5d)
353 Consider a message as undeliverable, when delivery fails with a
354 temporary error, and the time in the queue has reached the maxi‐
355 mal_queue_lifetime limit.
356 queue_run_delay (300s)
358 The time between deferred queue scans by the queue manager;
359 prior to Postfix 2.4 the default value was 1000s.
360 transport_retry_time (60s)
362 The time between attempts by the Postfix queue manager to con‐
363 tact a malfunctioning message delivery transport.
364 Available in Postfix version 2.1 and later:
366 bounce_queue_lifetime (5d)
368 Consider a bounce message as undeliverable, when delivery fails
369 with a temporary error, and the time in the queue has reached
370 the bounce_queue_lifetime limit.
371 Available in Postfix version 2.5 and later:
373 default_destination_rate_delay (0s)
375 The default amount of delay that is inserted between individual
376 deliveries to the same destination; the resulting behavior
377 depends on the value of the corresponding per-destination recip‐
378 ient limit.
379 transport_destination_rate_delay ($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 Available in Postfix version 3.1 and later:
386 default_transport_rate_delay (0s)
388 The default amount of delay that is inserted between individual
389 deliveries over the same message delivery transport, regardless
390 of destination.
391 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
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 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 Available in Postfix version 3.1 and later:
408 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
414 config_directory (see 'postconf -d' output)
415 The default location of the Postfix main.cf and master.cf con‐
416 figuration files.
417 defer_transports (empty)
419 The names of message delivery transports that should not deliver
420 mail unless someone issues "sendmail -q" or equivalent.
421 delay_logging_resolution_limit (2)
423 The maximal number of digits after the decimal point when log‐
424 ging sub-second delay values.
425 helpful_warnings (yes)
427 Log warnings about problematic configuration settings, and pro‐
428 vide helpful suggestions.
429 process_id (read-only)
431 The process ID of a Postfix command or daemon process.
432 process_name (read-only)
434 The process name of a Postfix command or daemon process.
435 queue_directory (see 'postconf -d' output)
437 The location of the Postfix top-level queue directory.
438 syslog_facility (mail)
440 The syslog facility of Postfix logging.
441 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 Available in Postfix version 3.0 and later:
447 confirm_delay_cleared (no)
449 After sending a "your message is delayed" notification, inform
450 the sender when the delay clears up.
451 Available in Postfix 3.3 and later:
453 service_name (read-only)
455 The master.cf service name of a Postfix daemon process.
456
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
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 syslogd(8), system logging
472
474 Use "postconf readme_directory" or "postconf html_directory" to locate
475 this information.
476 SCHEDULER_README, scheduling algorithm
477 QSHAPE_README, Postfix queue analysis
478
480 The Secure Mailer license must be distributed with this software.
481
483 Wietse Venema
484 IBM T.J. Watson Research
485 P.O. Box 704
486 Yorktown Heights, NY 10598, USA
487 Preemptive scheduler enhancements:
489 Patrik Rak
490 Modra 6
491 155 00, Prague, Czech Republic
492 Wietse Venema
494 Google, Inc.
495 111 8th Avenue
496 New York, NY 10011, USA
497 QMGR(8)