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 $default_filter_nexthop instead; when
181 that value is empty, use the domain in the recipient address.
182
184 qmgr_clog_warn_time (300s)
185 The minimal delay between warnings that a specific destination
186 is clogging up the Postfix active queue.
187 qmgr_message_active_limit (20000)
189 The maximal number of messages in the active queue.
190 qmgr_message_recipient_limit (20000)
192 The maximal number of recipients held in memory by the Postfix
193 queue manager, and the maximal size of the size of the short-
194 term, in-memory "dead" destination status cache.
195 qmgr_message_recipient_minimum (10)
197 The minimal number of in-memory recipients for any message.
198 default_recipient_limit (20000)
200 The default per-transport upper limit on the number of in-memory
201 recipients.
202 transport_recipient_limit ($default_recipient_limit)
204 Idem, for delivery via the named message transport.
205 default_extra_recipient_limit (1000)
207 The default value for the extra per-transport limit imposed on
208 the number of in-memory recipients.
209 transport_extra_recipient_limit ($default_extra_recipient_limit)
211 Idem, for delivery via the named message transport.
212 Available in Postfix version 2.4 and later:
214 default_recipient_refill_limit (100)
216 The default per-transport limit on the number of recipients
217 refilled at once.
218 transport_recipient_refill_limit ($default_recipient_refill_limit)
220 Idem, for delivery via the named message transport.
221 default_recipient_refill_delay (5s)
223 The default per-transport maximum delay between recipients
224 refills.
225 transport_recipient_refill_delay ($default_recipient_refill_delay)
227 Idem, for delivery via the named message transport.
228
230 initial_destination_concurrency (5)
231 The initial per-destination concurrency level for parallel
232 delivery to the same destination.
233 default_destination_concurrency_limit (20)
235 The default maximal number of parallel deliveries to the same
236 destination.
237 transport_destination_concurrency_limit ($default_destination_concur‐
239 rency_limit)
240 Idem, for delivery via the named message transport.
241 Available in Postfix version 2.5 and later:
243 transport_initial_destination_concurrency ($initial_destination_concur‐
245 rency)
246 Initial concurrency for delivery via the named message trans‐
247 port.
248 default_destination_concurrency_failed_cohort_limit (1)
250 How many pseudo-cohorts must suffer connection or handshake
251 failure before a specific destination is considered unavailable
252 (and further delivery is suspended).
253 transport_destination_concurrency_failed_cohort_limit ($default_desti‐
255 nation_concurrency_failed_cohort_limit)
256 Idem, for delivery via the named message transport.
257 default_destination_concurrency_negative_feedback (1)
259 The per-destination amount of delivery concurrency negative
260 feedback, after a delivery completes with a connection or hand‐
261 shake failure.
262 transport_destination_concurrency_negative_feedback ($default_destina‐
264 tion_concurrency_negative_feedback)
265 Idem, for delivery via the named message transport.
266 default_destination_concurrency_positive_feedback (1)
268 The per-destination amount of delivery concurrency positive
269 feedback, after a delivery completes without connection or hand‐
270 shake failure.
271 transport_destination_concurrency_positive_feedback ($default_destina‐
273 tion_concurrency_positive_feedback)
274 Idem, for delivery via the named message transport.
275 destination_concurrency_feedback_debug (no)
277 Make the queue manager's feedback algorithm verbose for perfor‐
278 mance analysis purposes.
279
281 default_destination_recipient_limit (50)
282 The default maximal number of recipients per message delivery.
283 transport_destination_recipient_limit ($default_destination_recipi‐
285 ent_limit)
286 Idem, for delivery via the named message transport.
287
289 default_delivery_slot_cost (5)
290 How often the Postfix queue manager's scheduler is allowed to
291 preempt delivery of one message with another.
292 transport_delivery_slot_cost ($default_delivery_slot_cost)
294 Idem, for delivery via the named message transport.
295 default_minimum_delivery_slots (3)
297 How many recipients a message must have in order to invoke the
298 Postfix queue manager's scheduling algorithm at all.
299 transport_minimum_delivery_slots ($default_minimum_delivery_slots)
301 Idem, for delivery via the named message transport.
302 default_delivery_slot_discount (50)
304 The default value for transport-specific _delivery_slot_discount
305 settings.
306 transport_delivery_slot_discount ($default_delivery_slot_discount)
308 Idem, for delivery via the named message transport.
309 default_delivery_slot_loan (3)
311 The default value for transport-specific _delivery_slot_loan
312 settings.
313 transport_delivery_slot_loan ($default_delivery_slot_loan)
315 Idem, for delivery via the named message transport.
316
318 minimal_backoff_time (300s)
319 The minimal time between attempts to deliver a deferred message;
320 prior to Postfix 2.4 the default value was 1000s.
321 maximal_backoff_time (4000s)
323 The maximal time between attempts to deliver a deferred message.
324 maximal_queue_lifetime (5d)
326 The maximal time a message is queued before it is sent back as
327 undeliverable.
328 queue_run_delay (300s)
330 The time between deferred queue scans by the queue manager;
331 prior to Postfix 2.4 the default value was 1000s.
332 transport_retry_time (60s)
334 The time between attempts by the Postfix queue manager to con‐
335 tact a malfunctioning message delivery transport.
336 Available in Postfix version 2.1 and later:
338 bounce_queue_lifetime (5d)
340 The maximal time a bounce message is queued before it is consid‐
341 ered undeliverable.
342 Available in Postfix version 2.5 and later:
344 default_destination_rate_delay (0s)
346 The default amount of delay that is inserted between individual
347 deliveries to the same destination; with per-destination recipi‐
348 ent limit > 1, a destination is a domain, otherwise it is a
349 recipient.
350 transport_destination_rate_delay $default_destination_rate_delay
352 Idem, for delivery via the named message transport.
353
355 config_directory (see 'postconf -d' output)
356 The default location of the Postfix main.cf and master.cf con‐
357 figuration files.
358 defer_transports (empty)
360 The names of message delivery transports that should not deliver
361 mail unless someone issues "sendmail -q" or equivalent.
362 delay_logging_resolution_limit (2)
364 The maximal number of digits after the decimal point when log‐
365 ging sub-second delay values.
366 helpful_warnings (yes)
368 Log warnings about problematic configuration settings, and pro‐
369 vide helpful suggestions.
370 ipc_timeout (3600s)
372 The time limit for sending or receiving information over an
373 internal communication channel.
374 process_id (read-only)
376 The process ID of a Postfix command or daemon process.
377 process_name (read-only)
379 The process name of a Postfix command or daemon process.
380 queue_directory (see 'postconf -d' output)
382 The location of the Postfix top-level queue directory.
383 syslog_facility (mail)
385 The syslog facility of Postfix logging.
386 syslog_name (see 'postconf -d' output)
388 The mail system name that is prepended to the process name in
389 syslog records, so that "smtpd" becomes, for example, "post‐
390 fix/smtpd".
391
393 /var/spool/postfix/incoming, incoming queue
394 /var/spool/postfix/active, active queue
395 /var/spool/postfix/deferred, deferred queue
396 /var/spool/postfix/bounce, non-delivery status
397 /var/spool/postfix/defer, non-delivery status
398 /var/spool/postfix/trace, delivery status
399
401 trivial-rewrite(8), address routing
402 bounce(8), delivery status reports
403 postconf(5), configuration parameters
404 master(5), generic daemon options
405 master(8), process manager
406 syslogd(8), system logging
407
409 Use "postconf readme_directory" or "postconf html_directory" to locate
410 this information.
411 SCHEDULER_README, scheduling algorithm
412 QSHAPE_README, Postfix queue analysis
413
415 The Secure Mailer license must be distributed with this software.
416
418 Wietse Venema
419 IBM T.J. Watson Research
420 P.O. Box 704
421 Yorktown Heights, NY 10598, USA
422 Preemptive scheduler enhancements:
424 Patrik Rak
425 Modra 6
426 155 00, Prague, Czech Republic
427 QMGR(8)