This is the Postfix 3.6 (stable) release. The stable Postfix release is called postfix-3.6.x where 3=major release number, 6=minor release number, x=patchlevel. The stable release never changes except for patches that address bugs or emergencies. Patches change the patchlevel and the release date. New features are developed in snapshot releases. These are called postfix-3.7-yyyymmdd where yyyymmdd is the release date (yyyy=year, mm=month, dd=day). Patches are never issued for snapshot releases; instead, a new snapshot is released. The mail_release_date configuration parameter (format: yyyymmdd) specifies the release date of a stable release or snapshot release. If you upgrade from Postfix 3.4 or earlier, read RELEASE_NOTES-3.5 before proceeding. License change --------------- This software is distributed with a dual license: in addition to the historical IBM Public License 1.0, it is now also distributed with the more recent Eclipse Public License 2.0. Recipients can choose to take the software under the license of their choice. Those who are more comfortable with the IPL can continue with that license. Major changes - internal protocol identification ------------------------------------------------ [Incompat 20200920] Internal protocols have changed. You need to "postfix stop" before updating, or before backing out to an earlier release, otherwise long-running daemons (pickup, qmgr, verify, tlsproxy, postscreen) may fail to communicate with the rest of Postfix, causing mail delivery delays until Postfix is restarted. This change does not affect message files in Postfix queue directories, only the communication between running Postfix programs. With this change, every Postfix internal service, including the postdrop command, announces the name of its protocol before doing any other I/O. Every Postfix client program, including the Postfix sendmail command, will verify that the protocol name matches what it is supposed to be. The purpose of this change is to produce better error messages, for example, when someone configures the discard daemon as a bounce service in master.cf, or vice versa. This change may break third-party programs that implement a Postfix-internal protocol such as qpsmtpd. Such programs have never been supported. Fortunately, this will be an easy fix: look at the first data from the cleanup daemon: if it is a protocol announcement, you're talking to Postfix 3.6 or later. That's the only real change. Major changes - tls ------------------- [Incompat 20200705] The minimum supported OpenSSL version is 1.1.1, which will reach the end of life by 2023-09-11. Postfix 3.6 is expected to reach the end of support in 2025. Until then, Postfix will be updated as needed for compatibility with OpenSSL. The default fingerprint digest has changed from md5 to sha256 (Postfix 3.6 with compatibility_level >= 3.6). With a lower compatibility_level setting, Postfix defaults to using md5, and logs a warning when a Postfix configuration specifies no explicit digest type. Export-grade Diffie-Hellman key exchange is no longer supported, and the tlsproxy_tls_dh512_param_file parameter is ignored, [Feature 20200906] The tlstype.pl helper script by Viktor Dukhovni reports TLS information per message delivery. This processes output from the collate.pl script. See auxiliary/collate/README.tlstype and auxiliary/collate/tlstype.pl. Major changes - compatibility level ----------------------------------- [Feature 20210109] Starting with Postfix version 3.6, the compatibility level is "3.6". In future Postfix releases, the compatibility level will be the Postfix version that introduced the last incompatible change. The level is formatted as 'major.minor.patch', where 'patch' is usually omitted and defaults to zero. Earlier compatibility levels are 0, 1 and 2. This also introduces main.cf and master.cf support for the <=level, " which matches an empty sender address, and the "@domain" wildcard pattern. More information about those can be found in the postconf(5) manpage. Example: /etc/postfix/main.cf: # Allow root and postfix full control, anyone else can only # send mail as themselves. Use "uid:" followed by the numerical # UID when the UID has no entry in the UNIX password file. local_login_sender_maps = inline:{ { root = *}, { postfix = * } }, pcre:/etc/postfix/login_senders /etc/postfix/login_senders: # Allow both the bare username and the user@domain forms. /(.+)/ $1 $1@example.com Major changes - order of relay and recipient restrictions --------------------------------------------------------- [Incompat 20210131] With smtpd_relay_before_recipient_restrictions=yes, the Postfix SMTP server will evaluate smtpd_relay_restrictions before smtpd_recipient_restrictions. This is the default behavior with compatibility_level >= 3.6. This change makes the implemented behavior consistent with existing documentation. There is a backwards-compatibility warning that allows users to freeze historical behavior. See COMPATIBILITY_README for details. Major changes - respectful logging ---------------------------------- [Feature 20210220] Postfix version 3.6 deprecates terminology that implies white is better than black. Instead, Postfix prefers 'allowlist', 'denylist', and variations on those words. This change affects Postfix documentation, and postscreen parameters and logging. To keep the old postscreen logging set "respectful_logging = no" in main.cf. Noel Jones assisted with the initial transition. Changes in documentation ------------------------ Postfix documentation was updated to use 'allowlist', 'denylist', etc. These documentation changes do not affect Postfix behavior. Changes in parameter names -------------------------- The following postscreen parameters replace names that contain 'blacklist' or 'whitelist': postscreen_allowlist_interfaces postscreen_denylist_action postscreen_dnsbl_allowlist_threshold These new parameters have backwards-compatible default settings that support the old parameter names, so that the name change should not affect Postfix behavior. This means that existing management tools that use the old parameter names should keep working as before. This compatibility safety net may break when some management tools use the new parameter names, and some use the old names, such that different tools will disagree on how Postfix works. Changes in logging ------------------ The following logging replaces forms that contain 'blacklist' or 'whitelist': postfix/postscreen[pid]: ALLOWLIST VETO [address]:port postfix/postscreen[pid]: ALLOWLISTED [address]:port postfix/postscreen[pid]: DENYLISTED [address]:port To avoid breaking logfile analysis tools, Postfix keeps logging the old forms by default, as long as the compatibility_level parameter setting is less than 3.6, and the respectful_logging parameter is not explicitly configured. As a reminder, Postfix will log the following: postfix/postscreen[pid]: Using backwards-compatible default setting respectful_logging=no for client [address]:port To keep logging the old form, make the setting "respectful_logging = no" permanent in main.cf, for example: # postconf "respectful_logging = no" # postfix reload To stop the reminder, configure the respectful_logging parameter to "yes" or "no", or configure "compatibility_level = 3.6". Major changes - threaded bounces -------------------------------- [Feature 20201205] Support for threaded bounces. This allows mail readers to present a non-delivery, delayed delivery, or successful delivery notification in the same email thread as the original message. Unfortunately, this also makes it easy for users to mistakenly delete the whole email thread (all related messages), instead of deleting only the delivery status notification. To enable, specify "enable_threaded_bounces = yes". Other changes - smtpd_sasl_mechanism_list ----------------------------------------- [Feature 20200906] The smtpd_sasl_mechanism_list parameter (default: !external, static:rest) prevents confusing errors when a SASL backend announces EXTERNAL support which Postfix does not support. Other changes - delivery logging -------------------------------- [Incompat 20200531] Postfix delivery agents now log an explicit record when delegating delivery to a different Postfix delivery agent. For example, with "best_mx_transport = local", an SMTP delivery agent will now log when a recipient will be delivered locally. This makes the delegating delivery agent visible, where it would otherwise have remained invisible, which would complicate troubleshooting. postfix/smtp[pid]: queueid: passing to transport=local This will usually be followed by logging for an actual delivery: postfix/local[pid]: queueid: to=, relay=local, ... Other examples: the local delivery agent will log a record that it defers mailbox delivery through mailbox_transport or through fallback_transport. Other changes - error logging ----------------------------- [Incompat 20200531] Postfix programs will now log "Application error" instead of "Success" or "Unknown error: 0" when an operation fails with errno == 0, i.e., the error originates from non-kernel code. Other changes - dns lookups --------------------------- [Feature 20200509] The threadsafe resolver API (res_nxxx() calls) is now the default, not because the API is threadsafe, but because this is the API where new features are being added. To build old style, build with: make makefiles CCARGS="-DNO_RES_NCALLS..." This is the default for systems that are known not to support the threadsafe resolver API.