The stable Postfix release is called postfix-2.4.x where 2=major
release number, 4=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-2.5-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.

Incompatibility with Postfix 2.3 and earlier
============================================

If you upgrade from Postfix 2.3 or earlier, read RELEASE_NOTES-2.4
before proceeding.

Incompatibility with Postfix snapshot 2007XXXX
==============================================

The default sender address for address verification probes was
changed from "postmaster" to "double-bounce", so that the Postfix
SMTP server no longer causes surprising behavior by excluding
"postmaster" from SMTP server access controls.

Incompatibility with Postfix snapshot 20070422
==============================================

When the pipe(8) delivery agent is configured to create the optional
Delivered-To: header, it now first checks if that same header is
already present in the message. If so, the message is returned as
undeliverable. This test should have been included with Postfix 2.0
when Delivered-To: support was added to the pipe(8) delivery agent.