This is the Postfix 3.9 experimental release.

The stable Postfix release is called postfix-3.8.x where 3=major
release number, 8=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-3.9-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 3.7 or earlier, please read RELEASE_NOTES-3.8
before proceeding.

Dual license
------------

As of Postfix 3.2.5 this software is distributed with a dual license:
in addition to the historical IBM Public License (IPL) 1.0, it is
now also distributed with the more recent Eclipse Public License
(EPL) 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.

Incompatible changes with snapshot 20230603
===========================================

Security: the Postfix SMTP server by default disconnects remote
SMTP clients that violate RFC 2920 (or 5321) command pipelining
constraints. The server replies with "421 4.7.0 Error: SMTP protocol
synchronization" and logs the unexpected remote SMTP client input.
Specify "smtpd_reject_unauth_pipelining = no" to disable.

Major changes with snapshot 20230522
====================================

Preliminary support for OpenSSL configuration files, primarily
OpenSSL 1.1.1b and later. This introduces two new parameters
"tls_config_file" and "tls_config_name", which can be used to limit
collateral damage from OS distributions that crank up security to
11, increasing the number of plaintext email deliveries. Details
are in the postconf(5) manpage under "tls_config_file" and
"tls_config_name".

Incompatible changes with snapshot 20230419
===========================================

The MySQL client default characterset is now configurable with the
"charset" configuration file attribute. The default is "utf8mb4",
consistent with the MySQL 8.0 built-in default, but different from
earlier MySQL versions where the built-in default was "latin1".