Postfix was released under the IBM Public License. All Postfix source code is signed with Wietse's PGP key.
Official releases do not change except for bugfixes and for portability fixes. New features are tested out in experimental releases (see below).
Postfix 2.2 Patchlevel 2 Source code | PGP signature | Release notes | Change log
Official releases are called "Postfix a.b.c", where a is the major release number, b is the minor release number, and c is the patchlevel.
Source code changes since Postfix Version 2.2.0.
New features are tested in experimental releases. They become part of the next official release once the code has not changed for a significant amount of time. Although this code is still subject to change, it runs on all of Wietse's systems so it is production quality.
Postfix 2.3 Snapshot 20050402 Source code | PGP signature | Release notes | Change log
Experimental releases are called "Postfix a.b-yyyymmdd", where a.b is the next official Postfix release and yyyymmdd is the release date.
Postfix 2.1 Patchlevel 05 Source code | PGP signature
Postfix 2.0 Patchlevel 20 Source code | PGP signature
Patch to black-list domain names by their mail servers (such as Verisign's mail sink) or by their DNS servers (second revision: don't defer mail when DNS lookup fails; lookup grandparent NS records).
Postfix 1.1 Patchlevel 13 Source code | PGP signature
Postfix 1.0 Patchlevel 08 Source code | PGP signature (released as version 20010228)
Version 19991231 Patchlevel 13 Source code | PGP signature
Version 19990906 Patchlevel 09 Source code | PGP signature