This is the Postfix 3.3 (stable) release.

The stable Postfix release is called postfix-3.3.x where 3=major
release number, 3=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-3.4-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 3.1 or earlier, read RELEASE_NOTES-3.2
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 - compatibility safety net
----------------------------------------

[20180106] With compatibility_level < 1, the Postfix SMTP server
now warns for mail that would be blocked by the Postfix 2.10
smtpd_relay_restrictions feature, without blocking that mail. This
extends the compatibility safety net for sites that upgrade from
earlier Postfix versions (questions on the postfix-users list show
there is a steady trickle). See COMPATIBILITY_README for details.

Major changes - configuration
-----------------------------

[20170617] The postconf command now warns about unknown parameter
names in a Postfix database configuration file. As with other unknown
parameter names, these warnings can help to find typos early.

[20180113] New read-only service_name parameter that contains the
master.cf service name of a Postfix daemon process (it that is empty
in a non-daemon process). This can make Postfix SMTP server logging
logging distinct by setting the syslog_name in master.cf with "-o
syslog_name=postfix/$service_name" for the "submission" and "smtps"
services, and can make Postfix SMTP client distinct by setting "-o
syslog_name=postfix/$service_name" for the "relay" service.

Major changes - container support
---------------------------------

[20171218] Preliminary support to run Postfix in the foreground,
with "postfix start-fg". This requires that Postfix multi-instance
support is disabled. To receive Postfix syslog information on the
container's host, mount the host's /dev/log socket inside the
container (example: "docker run -v /dev/log:/dev/log ..."), and
specify a distinct Postfix "syslog_name" prefix that identifies the
logging from the Postfix instance. Postfix does not log systemd
events.

Major changes - database support
---------------------------------

[20170617] The postconf command warns about unknown parameter names
in a Postfix database configuration file.

[20171227] The pgsql_table(5) hosts parameter now supports the
postgresql:// URI syntax. Contributed by Magosányi Árpád.

Major changes - header format
-----------------------------

[20180010] This release changes the format of 'full name' information
in Postfix-generated From: headers, when a local program such as
/bin/mail submits a message without From: header.

Postfix-generated From: headers with 'full name' information are
now formatted as "From: name <address>" by default. Specify
"header_from_format = obsolete" to get the earlier form "From:
address (name)". See the postconf(5) manpage for more details.

Major changes - invisible changes
---------------------------------

[20170617] Additional paranoia in the VSTRING implementation: a
null byte after the end of vstring buffers (this is a safety net
so that C-style string operations won't scribble past the end);
earlier detection of bad length and precision format string specifiers
(these are the result of programming error, as Postfix format strings
cannot be specified externally).

Major changes - milter support
------------------------------

[20171223] Milter applications can now send RET and ENVID parameters
in SMFIR_CHGFROM (change envelope sender) requests.

Major changes - mixed IPv6/IPv4 support
---------------------------------------

[20170505] Workaround for mail delivery problems when 1) both Postfix
IPv6 and IPv4 support are enabled, 2) some destination announces
more primary IPv6 MX addresses than primary IPv4 MX addresses, 3)
the destination is unreachable over IPv6, and 4) Postfix runs into
the smtp_mx_address_limit before it can try to deliver over IPv4.

When both Postfix IPv6 and IPv4 support are enabled, the Postfix
SMTP client will now relax MX preferences so that it can schedule
similar numbers of IPv4 and IPv6 destination addresses. This ensures
that an IPv6 connectivity problem will not prevent mail from being
delivered over IPv4 (and vice versa). Specify "smtp_balance_inet_protocols
= no" to disable this workaround.

Major changes - xclient
-----------------------

[20171218] The Postfix SMTP server now allows the XCLIENT command
before STARTTLS when TLS is required. This is useful for servers
that run behind a reverse proxy server such as nginx.