The stable Postfix release is called postfix-2.3.x where 2=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-2.4-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.

Incompatibility with Postfix 2.2 and earlier
============================================

If you upgrade from Postfix 2.2 or earlier, read RELEASE_NOTES-2.3
before proceeding.

Incompatible changes with Postfix snapshot 20061019-QMGR
========================================================

After upgrading Postfix you MUST execute "postfix reload", otherwise
the queue manager may log a warnings with:

    warning: connect to transport retry: Connection refused

The upgrade procedure adds a new "retry" service to the master.cf
file.  If you make the mistake of copying old Postfix configuration
files over the new files, the queue manager may log warnings with:

    warning: connect to transport retry: Connection refused

To fix your master.cf file, use "postfix upgrade-configuration"
followed by "postfix reload".

Incompatible changes with Postfix snapshot 20061006
===================================================

The format of SMTP server TLS session cache lookup keys has changed.
The lookup key now includes the master.cf service name.

Incompatible changes with Postfix snapshot 20060806
===================================================

Postfix no longer announces its name in delivery status notifications.
Users believe that Wietse provides a free help desk service that
solves all their email problems.