1SMTP(8) System Manager's Manual SMTP(8)
2
6 smtp - Postfix SMTP+LMTP client
7
9 smtp [generic Postfix daemon options] [flags=DORX]
10
12 The Postfix SMTP+LMTP client implements the SMTP and LMTP mail delivery
13 protocols. It processes message delivery requests from the queue man‐
14 ager. Each request specifies a queue file, a sender address, a domain
15 or host to deliver to, and recipient information. This program expects
16 to be run from the master(8) process manager.
17 The SMTP+LMTP client updates the queue file and marks recipients as
19 finished, or it informs the queue manager that delivery should be tried
20 again at a later time. Delivery status reports are sent to the
21 bounce(8), defer(8) or trace(8) daemon as appropriate.
22 The SMTP+LMTP client looks up a list of mail exchanger addresses for
24 the destination host, sorts the list by preference, and connects to
25 each listed address until it finds a server that responds.
26 When a server is not reachable, or when mail delivery fails due to a
28 recoverable error condition, the SMTP+LMTP client will try to deliver
29 the mail to an alternate host.
30 After a successful mail transaction, a connection may be saved to the
32 scache(8) connection cache server, so that it may be used by any
33 SMTP+LMTP client for a subsequent transaction.
34 By default, connection caching is enabled temporarily for destinations
36 that have a high volume of mail in the active queue. Connection caching
37 can be enabled permanently for specific destinations.
38
40 The Postfix SMTP+LMTP client supports multiple destinations separated
41 by comma or whitespace (Postfix 3.5 and later). SMTP destinations have
42 the following form:
43 domainname
45 domainname:port
47 Look up the mail exchangers for the specified domain, and con‐
48 nect to the specified port (default: smtp).
49 [hostname]
51 [hostname]:port
53 Look up the address(es) of the specified host, and connect to
54 the specified port (default: smtp).
55 [address]
57 [address]:port
59 Connect to the host at the specified address, and connect to the
60 specified port (default: smtp). An IPv6 address must be format‐
61 ted as [ipv6:address].
62
64 The Postfix SMTP+LMTP client supports multiple destinations separated
65 by comma or whitespace (Postfix 3.5 and later). LMTP destinations have
66 the following form:
67 unix:pathname
69 Connect to the local UNIX-domain server that is bound to the
70 specified pathname. If the process runs chrooted, an absolute
71 pathname is interpreted relative to the Postfix queue directory.
72 inet:hostname
74 inet:hostname:port
76 inet:[address]
78 inet:[address]:port
80 Connect to the specified TCP port on the specified local or re‐
81 mote host. If no port is specified, connect to the port defined
82 as lmtp in services(4). If no such service is found, the
83 lmtp_tcp_port configuration parameter (default value of 24) will
84 be used. An IPv6 address must be formatted as [ipv6:address].
85
87 By default, the Postfix SMTP+LMTP client delivers mail to multiple re‐
88 cipients per delivery request. This is undesirable when prepending a
89 Delivered-to: or X-Original-To: message header. To prevent Postfix from
90 sending multiple recipients per delivery request, specify
91 transport_destination_recipient_limit = 1
93 in the Postfix main.cf file, where transport is the name in the first
95 column of the Postfix master.cf entry for this mail delivery service.
96
98 flags=DORX (optional)
99 Optional message processing flags.
100 D Prepend a "Delivered-To: recipient" message header with
102 the envelope recipient address. Note: for this to work,
103 the transport_destination_recipient_limit must be 1 (see
104 SINGLE-RECIPIENT DELIVERY above for details).
105 The D flag also enforces loop detection: if a message al‐
107 ready contains a Delivered-To: header with the same re‐
108 cipient address, then the message is returned as undeliv‐
109 erable. The address comparison is case insensitive.
110 This feature is available as of Postfix 3.5.
112 O Prepend an "X-Original-To: recipient" message header with
114 the recipient address as given to Postfix. Note: for this
115 to work, the transport_destination_recipient_limit must
116 be 1 (see SINGLE-RECIPIENT DELIVERY above for details).
117 This feature is available as of Postfix 3.5.
119 R Prepend a "Return-Path: <sender>" message header with the
121 envelope sender address.
122 This feature is available as of Postfix 3.5.
124 X Indicates that the delivery is final. This flag affects
126 the status reported in "success" DSN (delivery status no‐
127 tification) messages, and changes it from "relayed" into
128 "delivered".
129 This feature is available as of Postfix 3.5.
131
133 The SMTP+LMTP client is moderately security-sensitive. It
134 talks to SMTP or LMTP servers and to DNS servers on the
135 network. The SMTP+LMTP client can be run chrooted at fixed
136 low privilege.
137
139 RFC 821 (SMTP protocol)
140 RFC 822 (ARPA Internet Text Messages)
141 RFC 1651 (SMTP service extensions)
142 RFC 1652 (8bit-MIME transport)
143 RFC 1870 (Message Size Declaration)
144 RFC 2033 (LMTP protocol)
145 RFC 2034 (SMTP Enhanced Error Codes)
146 RFC 2045 (MIME: Format of Internet Message Bodies)
147 RFC 2046 (MIME: Media Types)
148 RFC 2554 (AUTH command)
149 RFC 2821 (SMTP protocol)
150 RFC 2920 (SMTP Pipelining)
151 RFC 3207 (STARTTLS command)
152 RFC 3461 (SMTP DSN Extension)
153 RFC 3463 (Enhanced Status Codes)
154 RFC 4954 (AUTH command)
155 RFC 5321 (SMTP protocol)
156 RFC 6531 (Internationalized SMTP)
157 RFC 6533 (Internationalized Delivery Status Notifications)
158 RFC 7672 (SMTP security via opportunistic DANE TLS)
159
161 Problems and transactions are logged to syslogd(8) or postlogd(8).
162 Corrupted message files are marked so that the queue manager can move
163 them to the corrupt queue for further inspection.
164 Depending on the setting of the notify_classes parameter, the postmas‐
166 ter is notified of bounces, protocol problems, and of other trouble.
167
169 SMTP and LMTP connection reuse for TLS (without closing the SMTP or
170 LMTP connection) is not supported before Postfix 3.4.
171 SMTP and LMTP connection reuse assumes that SASL credentials are valid
173 for all destinations that map onto the same IP address and TCP port.
174
176 Before Postfix version 2.3, the LMTP client is a separate program that
177 implements only a subset of the functionality available with SMTP:
178 there is no support for TLS, and connections are cached in-process,
179 making it ineffective when the client is used for multiple domains.
180 Most smtp_xxx configuration parameters have an lmtp_xxx "mirror" param‐
182 eter for the equivalent LMTP feature. This document describes only
183 those LMTP-related parameters that aren't simply "mirror" parameters.
184 Changes to main.cf are picked up automatically, as smtp(8) processes
186 run for only a limited amount of time. Use the command "postfix reload"
187 to speed up a change.
188 The text below provides only a parameter summary. See postconf(5) for
190 more details including examples.
191
193 ignore_mx_lookup_error (no)
194 Ignore DNS MX lookups that produce no response.
195 smtp_always_send_ehlo (yes)
197 Always send EHLO at the start of an SMTP session.
198 smtp_never_send_ehlo (no)
200 Never send EHLO at the start of an SMTP session.
201 smtp_defer_if_no_mx_address_found (no)
203 Defer mail delivery when no MX record resolves to an IP address.
204 smtp_line_length_limit (998)
206 The maximal length of message header and body lines that Postfix
207 will send via SMTP.
208 smtp_pix_workaround_delay_time (10s)
210 How long the Postfix SMTP client pauses before sending
211 ".<CR><LF>" in order to work around the PIX firewall
212 "<CR><LF>.<CR><LF>" bug.
213 smtp_pix_workaround_threshold_time (500s)
215 How long a message must be queued before the Postfix SMTP client
216 turns on the PIX firewall "<CR><LF>.<CR><LF>" bug workaround for
217 delivery through firewalls with "smtp fixup" mode turned on.
218 smtp_pix_workarounds (disable_esmtp, delay_dotcrlf)
220 A list that specifies zero or more workarounds for CISCO PIX
221 firewall bugs.
222 smtp_pix_workaround_maps (empty)
224 Lookup tables, indexed by the remote SMTP server address, with
225 per-destination workarounds for CISCO PIX firewall bugs.
226 smtp_quote_rfc821_envelope (yes)
228 Quote addresses in Postfix SMTP client MAIL FROM and RCPT TO
229 commands as required by RFC 5321.
230 smtp_reply_filter (empty)
232 A mechanism to transform replies from remote SMTP servers one
233 line at a time.
234 smtp_skip_5xx_greeting (yes)
236 Skip remote SMTP servers that greet with a 5XX status code.
237 smtp_skip_quit_response (yes)
239 Do not wait for the response to the SMTP QUIT command.
240 Available in Postfix version 2.0 and earlier:
242 smtp_skip_4xx_greeting (yes)
244 Skip SMTP servers that greet with a 4XX status code (go away,
245 try again later).
246 Available in Postfix version 2.2 and later:
248 smtp_discard_ehlo_keyword_address_maps (empty)
250 Lookup tables, indexed by the remote SMTP server address, with
251 case insensitive lists of EHLO keywords (pipelining, starttls,
252 auth, etc.) that the Postfix SMTP client will ignore in the EHLO
253 response from a remote SMTP server.
254 smtp_discard_ehlo_keywords (empty)
256 A case insensitive list of EHLO keywords (pipelining, starttls,
257 auth, etc.) that the Postfix SMTP client will ignore in the EHLO
258 response from a remote SMTP server.
259 smtp_generic_maps (empty)
261 Optional lookup tables that perform address rewriting in the
262 Postfix SMTP client, typically to transform a locally valid ad‐
263 dress into a globally valid address when sending mail across the
264 Internet.
265 Available in Postfix version 2.2.9 and later:
267 smtp_cname_overrides_servername (version dependent)
269 When the remote SMTP servername is a DNS CNAME, replace the
270 servername with the result from CNAME expansion for the purpose
271 of logging, SASL password lookup, TLS policy decisions, or TLS
272 certificate verification.
273 Available in Postfix version 2.3 and later:
275 lmtp_discard_lhlo_keyword_address_maps (empty)
277 Lookup tables, indexed by the remote LMTP server address, with
278 case insensitive lists of LHLO keywords (pipelining, starttls,
279 auth, etc.) that the Postfix LMTP client will ignore in the LHLO
280 response from a remote LMTP server.
281 lmtp_discard_lhlo_keywords (empty)
283 A case insensitive list of LHLO keywords (pipelining, starttls,
284 auth, etc.) that the Postfix LMTP client will ignore in the LHLO
285 response from a remote LMTP server.
286 Available in Postfix version 2.4.4 and later:
288 send_cyrus_sasl_authzid (no)
290 When authenticating to a remote SMTP or LMTP server with the de‐
291 fault setting "no", send no SASL authoriZation ID (authzid);
292 send only the SASL authentiCation ID (authcid) plus the auth‐
293 cid's password.
294 Available in Postfix version 2.5 and later:
296 smtp_header_checks (empty)
298 Restricted header_checks(5) tables for the Postfix SMTP client.
299 smtp_mime_header_checks (empty)
301 Restricted mime_header_checks(5) tables for the Postfix SMTP
302 client.
303 smtp_nested_header_checks (empty)
305 Restricted nested_header_checks(5) tables for the Postfix SMTP
306 client.
307 smtp_body_checks (empty)
309 Restricted body_checks(5) tables for the Postfix SMTP client.
310 Available in Postfix version 2.6 and later:
312 tcp_windowsize (0)
314 An optional workaround for routers that break TCP window scal‐
315 ing.
316 Available in Postfix version 2.8 and later:
318 smtp_dns_resolver_options (empty)
320 DNS Resolver options for the Postfix SMTP client.
321 Available in Postfix version 2.9 - 3.6:
323 smtp_per_record_deadline (no)
325 Change the behavior of the smtp_*_timeout time limits, from a
326 time limit per read or write system call, to a time limit to
327 send or receive a complete record (an SMTP command line, SMTP
328 response line, SMTP message content line, or TLS protocol mes‐
329 sage).
330 Available in Postfix version 2.9 and later:
332 smtp_send_dummy_mail_auth (no)
334 Whether or not to append the "AUTH=<>" option to the MAIL FROM
335 command in SASL-authenticated SMTP sessions.
336 Available in Postfix version 2.11 and later:
338 smtp_dns_support_level (empty)
340 Level of DNS support in the Postfix SMTP client.
341 Available in Postfix version 3.0 and later:
343 smtp_delivery_status_filter ($default_delivery_status_filter)
345 Optional filter for the smtp(8) delivery agent to change the de‐
346 livery status code or explanatory text of successful or unsuc‐
347 cessful deliveries.
348 smtp_dns_reply_filter (empty)
350 Optional filter for Postfix SMTP client DNS lookup results.
351 Available in Postfix version 3.3 and later:
353 smtp_balance_inet_protocols (yes)
355 When a remote destination resolves to a combination of IPv4 and
356 IPv6 addresses, ensure that the Postfix SMTP client can try both
357 address types before it runs into the smtp_mx_address_limit.
358 Available in Postfix 3.5 and later:
360 info_log_address_format (external)
362 The email address form that will be used in non-debug logging
363 (info, warning, etc.).
364 Available in Postfix 3.6 and later:
366 dnssec_probe (ns:.)
368 The DNS query type (default: "ns") and DNS query name (default:
369 ".") that Postfix may use to determine whether DNSSEC validation
370 is available.
371 known_tcp_ports (lmtp=24, smtp=25, smtps=submissions=465, submis‐
373 sion=587)
374 Optional setting that avoids lookups in the services(5) data‐
375 base.
376 Available in Postfix version 3.7 and later:
378 smtp_per_request_deadline (no)
380 Change the behavior of the smtp_*_timeout time limits, from a
381 time limit per plaintext or TLS read or write call, to a com‐
382 bined time limit for sending a complete SMTP request and for re‐
383 ceiving a complete SMTP response.
384 smtp_min_data_rate (500)
386 The minimum plaintext data transfer rate in bytes/second for
387 DATA requests, when deadlines are enabled with smtp_per_re‐
388 quest_deadline.
389 header_from_format (standard)
391 The format of the Postfix-generated From: header.
392
394 Available in Postfix version 2.0 and later:
395 disable_mime_output_conversion (no)
397 Disable the conversion of 8BITMIME format to 7BIT format.
398 mime_boundary_length_limit (2048)
400 The maximal length of MIME multipart boundary strings.
401 mime_nesting_limit (100)
403 The maximal recursion level that the MIME processor will handle.
404
406 Available in Postfix version 2.1 and later:
407 smtp_send_xforward_command (no)
409 Send the non-standard XFORWARD command when the Postfix SMTP
410 server EHLO response announces XFORWARD support.
411
413 smtp_sasl_auth_enable (no)
414 Enable SASL authentication in the Postfix SMTP client.
415 smtp_sasl_password_maps (empty)
417 Optional Postfix SMTP client lookup tables with one user‐
418 name:password entry per sender, remote hostname or next-hop do‐
419 main.
420 smtp_sasl_security_options (noplaintext, noanonymous)
422 Postfix SMTP client SASL security options; as of Postfix 2.3 the
423 list of available features depends on the SASL client implemen‐
424 tation that is selected with smtp_sasl_type.
425 Available in Postfix version 2.2 and later:
427 smtp_sasl_mechanism_filter (empty)
429 If non-empty, a Postfix SMTP client filter for the remote SMTP
430 server's list of offered SASL mechanisms.
431 Available in Postfix version 2.3 and later:
433 smtp_sender_dependent_authentication (no)
435 Enable sender-dependent authentication in the Postfix SMTP
436 client; this is available only with SASL authentication, and
437 disables SMTP connection caching to ensure that mail from dif‐
438 ferent senders will use the appropriate credentials.
439 smtp_sasl_path (empty)
441 Implementation-specific information that the Postfix SMTP client
442 passes through to the SASL plug-in implementation that is se‐
443 lected with smtp_sasl_type.
444 smtp_sasl_type (cyrus)
446 The SASL plug-in type that the Postfix SMTP client should use
447 for authentication.
448 Available in Postfix version 2.5 and later:
450 smtp_sasl_auth_cache_name (empty)
452 An optional table to prevent repeated SASL authentication fail‐
453 ures with the same remote SMTP server hostname, username and
454 password.
455 smtp_sasl_auth_cache_time (90d)
457 The maximal age of an smtp_sasl_auth_cache_name entry before it
458 is removed.
459 smtp_sasl_auth_soft_bounce (yes)
461 When a remote SMTP server rejects a SASL authentication request
462 with a 535 reply code, defer mail delivery instead of returning
463 mail as undeliverable.
464 Available in Postfix version 2.9 and later:
466 smtp_send_dummy_mail_auth (no)
468 Whether or not to append the "AUTH=<>" option to the MAIL FROM
469 command in SASL-authenticated SMTP sessions.
470
472 Detailed information about STARTTLS configuration may be found in the
473 TLS_README document.
474 smtp_tls_security_level (empty)
476 The default SMTP TLS security level for the Postfix SMTP client;
477 when a non-empty value is specified, this overrides the obsolete
478 parameters smtp_use_tls, smtp_enforce_tls, and smtp_tls_en‐
479 force_peername.
480 smtp_sasl_tls_security_options ($smtp_sasl_security_options)
482 The SASL authentication security options that the Postfix SMTP
483 client uses for TLS encrypted SMTP sessions.
484 smtp_starttls_timeout (300s)
486 Time limit for Postfix SMTP client write and read operations
487 during TLS startup and shutdown handshake procedures.
488 smtp_tls_CAfile (empty)
490 A file containing CA certificates of root CAs trusted to sign
491 either remote SMTP server certificates or intermediate CA cer‐
492 tificates.
493 smtp_tls_CApath (empty)
495 Directory with PEM format Certification Authority certificates
496 that the Postfix SMTP client uses to verify a remote SMTP server
497 certificate.
498 smtp_tls_cert_file (empty)
500 File with the Postfix SMTP client RSA certificate in PEM format.
501 smtp_tls_mandatory_ciphers (medium)
503 The minimum TLS cipher grade that the Postfix SMTP client will
504 use with mandatory TLS encryption.
505 smtp_tls_exclude_ciphers (empty)
507 List of ciphers or cipher types to exclude from the Postfix SMTP
508 client cipher list at all TLS security levels.
509 smtp_tls_mandatory_exclude_ciphers (empty)
511 Additional list of ciphers or cipher types to exclude from the
512 Postfix SMTP client cipher list at mandatory TLS security lev‐
513 els.
514 smtp_tls_dcert_file (empty)
516 File with the Postfix SMTP client DSA certificate in PEM format.
517 smtp_tls_dkey_file ($smtp_tls_dcert_file)
519 File with the Postfix SMTP client DSA private key in PEM format.
520 smtp_tls_key_file ($smtp_tls_cert_file)
522 File with the Postfix SMTP client RSA private key in PEM format.
523 smtp_tls_loglevel (0)
525 Enable additional Postfix SMTP client logging of TLS activity.
526 smtp_tls_note_starttls_offer (no)
528 Log the hostname of a remote SMTP server that offers STARTTLS,
529 when TLS is not already enabled for that server.
530 smtp_tls_policy_maps (empty)
532 Optional lookup tables with the Postfix SMTP client TLS security
533 policy by next-hop destination; when a non-empty value is speci‐
534 fied, this overrides the obsolete smtp_tls_per_site parameter.
535 smtp_tls_mandatory_protocols (see 'postconf -d' output)
537 TLS protocols that the Postfix SMTP client will use with manda‐
538 tory TLS encryption.
539 smtp_tls_scert_verifydepth (9)
541 The verification depth for remote SMTP server certificates.
542 smtp_tls_secure_cert_match (nexthop, dot-nexthop)
544 How the Postfix SMTP client verifies the server certificate
545 peername for the "secure" TLS security level.
546 smtp_tls_session_cache_database (empty)
548 Name of the file containing the optional Postfix SMTP client TLS
549 session cache.
550 smtp_tls_session_cache_timeout (3600s)
552 The expiration time of Postfix SMTP client TLS session cache in‐
553 formation.
554 smtp_tls_verify_cert_match (hostname)
556 How the Postfix SMTP client verifies the server certificate
557 peername for the "verify" TLS security level.
558 tls_daemon_random_bytes (32)
560 The number of pseudo-random bytes that an smtp(8) or smtpd(8)
561 process requests from the tlsmgr(8) server in order to seed its
562 internal pseudo random number generator (PRNG).
563 tls_high_cipherlist (see 'postconf -d' output)
565 The OpenSSL cipherlist for "high" grade ciphers.
566 tls_medium_cipherlist (see 'postconf -d' output)
568 The OpenSSL cipherlist for "medium" or higher grade ciphers.
569 tls_low_cipherlist (see 'postconf -d' output)
571 The OpenSSL cipherlist for "low" or higher grade ciphers.
572 tls_export_cipherlist (see 'postconf -d' output)
574 The OpenSSL cipherlist for "export" or higher grade ciphers.
575 tls_null_cipherlist (eNULL:!aNULL)
577 The OpenSSL cipherlist for "NULL" grade ciphers that provide au‐
578 thentication without encryption.
579 Available in Postfix version 2.4 and later:
581 smtp_sasl_tls_verified_security_options ($smtp_sasl_tls_security_op‐
583 tions)
584 The SASL authentication security options that the Postfix SMTP
585 client uses for TLS encrypted SMTP sessions with a verified
586 server certificate.
587 Available in Postfix version 2.5 and later:
589 smtp_tls_fingerprint_cert_match (empty)
591 List of acceptable remote SMTP server certificate fingerprints
592 for the "fingerprint" TLS security level (smtp_tls_secu‐
593 rity_level = fingerprint).
594 smtp_tls_fingerprint_digest (see 'postconf -d' output)
596 The message digest algorithm used to construct remote SMTP
597 server certificate fingerprints.
598 Available in Postfix version 2.6 and later:
600 smtp_tls_protocols (see postconf -d output)
602 TLS protocols that the Postfix SMTP client will use with oppor‐
603 tunistic TLS encryption.
604 smtp_tls_ciphers (medium)
606 The minimum TLS cipher grade that the Postfix SMTP client will
607 use with opportunistic TLS encryption.
608 smtp_tls_eccert_file (empty)
610 File with the Postfix SMTP client ECDSA certificate in PEM for‐
611 mat.
612 smtp_tls_eckey_file ($smtp_tls_eccert_file)
614 File with the Postfix SMTP client ECDSA private key in PEM for‐
615 mat.
616 Available in Postfix version 2.7 and later:
618 smtp_tls_block_early_mail_reply (no)
620 Try to detect a mail hijacking attack based on a TLS protocol
621 vulnerability (CVE-2009-3555), where an attacker prepends mali‐
622 cious HELO, MAIL, RCPT, DATA commands to a Postfix SMTP client
623 TLS session.
624 Available in Postfix version 2.8 and later:
626 tls_disable_workarounds (see 'postconf -d' output)
628 List or bit-mask of OpenSSL bug work-arounds to disable.
629 Available in Postfix version 2.11-3.1:
631 tls_dane_digest_agility (on)
633 Configure RFC7671 DANE TLSA digest algorithm agility.
634 tls_dane_trust_anchor_digest_enable (yes)
636 Enable support for RFC 6698 (DANE TLSA) DNS records that contain
637 digests of trust-anchors with certificate usage "2".
638 Available in Postfix version 2.11 and later:
640 smtp_tls_trust_anchor_file (empty)
642 Zero or more PEM-format files with trust-anchor certificates
643 and/or public keys.
644 smtp_tls_force_insecure_host_tlsa_lookup (no)
646 Lookup the associated DANE TLSA RRset even when a hostname is
647 not an alias and its address records lie in an unsigned zone.
648 tlsmgr_service_name (tlsmgr)
650 The name of the tlsmgr(8) service entry in master.cf.
651 Available in Postfix version 3.0 and later:
653 smtp_tls_wrappermode (no)
655 Request that the Postfix SMTP client connects using the legacy
656 SMTPS protocol instead of using the STARTTLS command.
657 Available in Postfix version 3.1 and later:
659 smtp_tls_dane_insecure_mx_policy (see 'postconf -d' output)
661 The TLS policy for MX hosts with "secure" TLSA records when the
662 nexthop destination security level is dane, but the MX record
663 was found via an "insecure" MX lookup.
664 Available in Postfix version 3.4 and later:
666 smtp_tls_connection_reuse (no)
668 Try to make multiple deliveries per TLS-encrypted connection.
669 smtp_tls_chain_files (empty)
671 List of one or more PEM files, each holding one or more private
672 keys directly followed by a corresponding certificate chain.
673 smtp_tls_servername (empty)
675 Optional name to send to the remote SMTP server in the TLS
676 Server Name Indication (SNI) extension.
677 Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:
679 tls_fast_shutdown_enable (yes)
681 A workaround for implementations that hang Postfix while shut‐
682 ting down a TLS session, until Postfix times out.
683
685 The following configuration parameters exist for compatibility with
686 Postfix versions before 2.3. Support for these will be removed in a fu‐
687 ture release.
688 smtp_use_tls (no)
690 Opportunistic mode: use TLS when a remote SMTP server announces
691 STARTTLS support, otherwise send the mail in the clear.
692 smtp_enforce_tls (no)
694 Enforcement mode: require that remote SMTP servers use TLS en‐
695 cryption, and never send mail in the clear.
696 smtp_tls_enforce_peername (yes)
698 With mandatory TLS encryption, require that the remote SMTP
699 server hostname matches the information in the remote SMTP
700 server certificate.
701 smtp_tls_per_site (empty)
703 Optional lookup tables with the Postfix SMTP client TLS usage
704 policy by next-hop destination and by remote SMTP server host‐
705 name.
706 smtp_tls_cipherlist (empty)
708 Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS
709 cipher list.
710
712 smtp_connect_timeout (30s)
713 The Postfix SMTP client time limit for completing a TCP connec‐
714 tion, or zero (use the operating system built-in time limit).
715 smtp_helo_timeout (300s)
717 The Postfix SMTP client time limit for sending the HELO or EHLO
718 command, and for receiving the initial remote SMTP server re‐
719 sponse.
720 lmtp_lhlo_timeout (300s)
722 The Postfix LMTP client time limit for sending the LHLO command,
723 and for receiving the initial remote LMTP server response.
724 smtp_xforward_timeout (300s)
726 The Postfix SMTP client time limit for sending the XFORWARD com‐
727 mand, and for receiving the remote SMTP server response.
728 smtp_mail_timeout (300s)
730 The Postfix SMTP client time limit for sending the MAIL FROM
731 command, and for receiving the remote SMTP server response.
732 smtp_rcpt_timeout (300s)
734 The Postfix SMTP client time limit for sending the SMTP RCPT TO
735 command, and for receiving the remote SMTP server response.
736 smtp_data_init_timeout (120s)
738 The Postfix SMTP client time limit for sending the SMTP DATA
739 command, and for receiving the remote SMTP server response.
740 smtp_data_xfer_timeout (180s)
742 The Postfix SMTP client time limit for sending the SMTP message
743 content.
744 smtp_data_done_timeout (600s)
746 The Postfix SMTP client time limit for sending the SMTP ".", and
747 for receiving the remote SMTP server response.
748 smtp_quit_timeout (300s)
750 The Postfix SMTP client time limit for sending the QUIT command,
751 and for receiving the remote SMTP server response.
752 Available in Postfix version 2.1 and later:
754 smtp_mx_address_limit (5)
756 The maximal number of MX (mail exchanger) IP addresses that can
757 result from Postfix SMTP client mail exchanger lookups, or zero
758 (no limit).
759 smtp_mx_session_limit (2)
761 The maximal number of SMTP sessions per delivery request before
762 the Postfix SMTP client gives up or delivers to a fall-back re‐
763 lay host, or zero (no limit).
764 smtp_rset_timeout (20s)
766 The Postfix SMTP client time limit for sending the RSET command,
767 and for receiving the remote SMTP server response.
768 Available in Postfix version 2.2 and earlier:
770 lmtp_cache_connection (yes)
772 Keep Postfix LMTP client connections open for up to $max_idle
773 seconds.
774 Available in Postfix version 2.2 and later:
776 smtp_connection_cache_destinations (empty)
778 Permanently enable SMTP connection caching for the specified
779 destinations.
780 smtp_connection_cache_on_demand (yes)
782 Temporarily enable SMTP connection caching while a destination
783 has a high volume of mail in the active queue.
784 smtp_connection_reuse_time_limit (300s)
786 The amount of time during which Postfix will use an SMTP connec‐
787 tion repeatedly.
788 smtp_connection_cache_time_limit (2s)
790 When SMTP connection caching is enabled, the amount of time that
791 an unused SMTP client socket is kept open before it is closed.
792 Available in Postfix version 2.3 and later:
794 connection_cache_protocol_timeout (5s)
796 Time limit for connection cache connect, send or receive opera‐
797 tions.
798 Available in Postfix version 2.9 - 3.6:
800 smtp_per_record_deadline (no)
802 Change the behavior of the smtp_*_timeout time limits, from a
803 time limit per read or write system call, to a time limit to
804 send or receive a complete record (an SMTP command line, SMTP
805 response line, SMTP message content line, or TLS protocol mes‐
806 sage).
807 Available in Postfix version 2.11 and later:
809 smtp_connection_reuse_count_limit (0)
811 When SMTP connection caching is enabled, the number of times
812 that an SMTP session may be reused before it is closed, or zero
813 (no limit).
814 Available in Postfix version 3.4 and later:
816 smtp_tls_connection_reuse (no)
818 Try to make multiple deliveries per TLS-encrypted connection.
819 Available in Postfix version 3.7 and later:
821 smtp_per_request_deadline (no)
823 Change the behavior of the smtp_*_timeout time limits, from a
824 time limit per plaintext or TLS read or write call, to a com‐
825 bined time limit for sending a complete SMTP request and for re‐
826 ceiving a complete SMTP response.
827 smtp_min_data_rate (500)
829 The minimum plaintext data transfer rate in bytes/second for
830 DATA requests, when deadlines are enabled with smtp_per_re‐
831 quest_deadline.
832 Implemented in the qmgr(8) daemon:
834 transport_destination_concurrency_limit ($default_destination_concur‐
836 rency_limit)
837 A transport-specific override for the default_destination_con‐
838 currency_limit parameter value, where transport is the master.cf
839 name of the message delivery transport.
840 transport_destination_recipient_limit ($default_destination_recipi‐
842 ent_limit)
843 A transport-specific override for the default_destination_recip‐
844 ient_limit parameter value, where transport is the master.cf
845 name of the message delivery transport.
846
848 Preliminary SMTPUTF8 support is introduced with Postfix 3.0.
849 smtputf8_enable (yes)
851 Enable preliminary SMTPUTF8 support for the protocols described
852 in RFC 6531..6533.
853 smtputf8_autodetect_classes (sendmail, verify)
855 Detect that a message requires SMTPUTF8 support for the speci‐
856 fied mail origin classes.
857 Available in Postfix version 3.2 and later:
859 enable_idna2003_compatibility (no)
861 Enable 'transitional' compatibility between IDNA2003 and
862 IDNA2008, when converting UTF-8 domain names to/from the ASCII
863 form that is used for DNS lookups.
864
866 debug_peer_level (2)
867 The increment in verbose logging level when a nexthop destina‐
868 tion, remote client or server name or network address matches a
869 pattern given with the debug_peer_list parameter.
870 debug_peer_list (empty)
872 Optional list of nexthop destination, remote client or server
873 name or network address patterns that, if matched, cause the
874 verbose logging level to increase by the amount specified in
875 $debug_peer_level.
876 error_notice_recipient (postmaster)
878 The recipient of postmaster notifications about mail delivery
879 problems that are caused by policy, resource, software or proto‐
880 col errors.
881 internal_mail_filter_classes (empty)
883 What categories of Postfix-generated mail are subject to be‐
884 fore-queue content inspection by non_smtpd_milters,
885 header_checks and body_checks.
886 notify_classes (resource, software)
888 The list of error classes that are reported to the postmaster.
889
891 best_mx_transport (empty)
892 Where the Postfix SMTP client should deliver mail when it de‐
893 tects a "mail loops back to myself" error condition.
894 config_directory (see 'postconf -d' output)
896 The default location of the Postfix main.cf and master.cf con‐
897 figuration files.
898 daemon_timeout (18000s)
900 How much time a Postfix daemon process may take to handle a re‐
901 quest before it is terminated by a built-in watchdog timer.
902 delay_logging_resolution_limit (2)
904 The maximal number of digits after the decimal point when log‐
905 ging sub-second delay values.
906 disable_dns_lookups (no)
908 Disable DNS lookups in the Postfix SMTP and LMTP clients.
909 inet_interfaces (all)
911 The network interface addresses that this mail system receives
912 mail on.
913 inet_protocols (see 'postconf -d output')
915 The Internet protocols Postfix will attempt to use when making
916 or accepting connections.
917 ipc_timeout (3600s)
919 The time limit for sending or receiving information over an in‐
920 ternal communication channel.
921 lmtp_assume_final (no)
923 When a remote LMTP server announces no DSN support, assume that
924 the server performs final delivery, and send "delivered" deliv‐
925 ery status notifications instead of "relayed".
926 lmtp_tcp_port (24)
928 The default TCP port that the Postfix LMTP client connects to.
929 max_idle (100s)
931 The maximum amount of time that an idle Postfix daemon process
932 waits for an incoming connection before terminating voluntarily.
933 max_use (100)
935 The maximal number of incoming connections that a Postfix daemon
936 process will service before terminating voluntarily.
937 process_id (read-only)
939 The process ID of a Postfix command or daemon process.
940 process_name (read-only)
942 The process name of a Postfix command or daemon process.
943 proxy_interfaces (empty)
945 The network interface addresses that this mail system receives
946 mail on by way of a proxy or network address translation unit.
947 smtp_address_preference (any)
949 The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP
950 client will try first, when a destination has IPv6 and IPv4 ad‐
951 dresses with equal MX preference.
952 smtp_bind_address (empty)
954 An optional numerical network address that the Postfix SMTP
955 client should bind to when making an IPv4 connection.
956 smtp_bind_address6 (empty)
958 An optional numerical network address that the Postfix SMTP
959 client should bind to when making an IPv6 connection.
960 smtp_helo_name ($myhostname)
962 The hostname to send in the SMTP HELO or EHLO command.
963 lmtp_lhlo_name ($myhostname)
965 The hostname to send in the LMTP LHLO command.
966 smtp_host_lookup (dns)
968 What mechanisms the Postfix SMTP client uses to look up a host's
969 IP address.
970 smtp_randomize_addresses (yes)
972 Randomize the order of equal-preference MX host addresses.
973 syslog_facility (mail)
975 The syslog facility of Postfix logging.
976 syslog_name (see 'postconf -d' output)
978 A prefix that is prepended to the process name in syslog
979 records, so that, for example, "smtpd" becomes "prefix/smtpd".
980 Available with Postfix 2.2 and earlier:
982 fallback_relay (empty)
984 Optional list of relay hosts for SMTP destinations that can't be
985 found or that are unreachable.
986 Available with Postfix 2.3 and later:
988 smtp_fallback_relay ($fallback_relay)
990 Optional list of relay hosts for SMTP destinations that can't be
991 found or that are unreachable.
992 Available with Postfix 3.0 and later:
994 smtp_address_verify_target (rcpt)
996 In the context of email address verification, the SMTP protocol
997 stage that determines whether an email address is deliverable.
998 Available with Postfix 3.1 and later:
1000 lmtp_fallback_relay (empty)
1002 Optional list of relay hosts for LMTP destinations that can't be
1003 found or that are unreachable.
1004 Available with Postfix 3.2 and later:
1006 smtp_tcp_port (smtp)
1008 The default TCP port that the Postfix SMTP client connects to.
1009 Available in Postfix 3.3 and later:
1011 service_name (read-only)
1013 The master.cf service name of a Postfix daemon process.
1014 Available in Postfix 3.7 and later:
1016 smtp_bind_address_enforce (no)
1018 Defer delivery when the Postfix SMTP client cannot apply the
1019 smtp_bind_address or smtp_bind_address6 setting.
1020
1022 generic(5), output address rewriting
1023 header_checks(5), message header content inspection
1024 body_checks(5), body parts content inspection
1025 qmgr(8), queue manager
1026 bounce(8), delivery status reports
1027 scache(8), connection cache server
1028 postconf(5), configuration parameters
1029 master(5), generic daemon options
1030 master(8), process manager
1031 tlsmgr(8), TLS session and PRNG management
1032 postlogd(8), Postfix logging
1033 syslogd(8), system logging
1034
1036 Use "postconf readme_directory" or "postconf html_directory" to locate
1037 this information.
1038 SASL_README, Postfix SASL howto
1039 TLS_README, Postfix STARTTLS howto
1040
1042 The Secure Mailer license must be distributed with this software.
1043
1045 Wietse Venema
1046 IBM T.J. Watson Research
1047 P.O. Box 704
1048 Yorktown Heights, NY 10598, USA
1049 Wietse Venema
1051 Google, Inc.
1052 111 8th Avenue
1053 New York, NY 10011, USA
1054 Command pipelining in cooperation with:
1056 Jon Ribbens
1057 Oaktree Internet Solutions Ltd.,
1058 Internet House,
1059 Canal Basin,
1060 Coventry,
1061 CV1 4LY, United Kingdom.
1062 SASL support originally by:
1064 Till Franke
1065 SuSE Rhein/Main AG
1066 65760 Eschborn, Germany
1067 TLS support originally by:
1069 Lutz Jaenicke
1070 BTU Cottbus
1071 Allgemeine Elektrotechnik
1072 Universitaetsplatz 3-4
1073 D-03044 Cottbus, Germany
1074 Revised TLS and SMTP connection cache support by:
1076 Victor Duchovni
1077 Morgan Stanley
1078 SMTP(8)