An on-line version of this announcement is available at http://www.postfix.org/announcements/postfix-2.6.0.html
Postfix stable release 2.6.0 is available. After Postfix was declared "complete" with version 2.3, the focus has moved towards improving the code/documentation, and updating it for changing environments.
Multi-instance support introduces a new postmulti(1) command to create/add/remove/etc. additional Postfix instances. The familiar "postfix start" etc. commands now automatically start multiple Postfix instances. The good news: nothing changes when you use only one Postfix instance. See MULTI_INSTANCE_README for details.
Multi-instance support required that some files be moved from the non-shared $config_directory to the shared $daemon_directory. The affected files are postfix-script, postfix-files and post-install.
TLS (SSL) support was updated for elliptic curve encryption. This requires OpenSSL version 0.9.9 or later. The SMTP client no longer uses the SSLv2 protocol by default. See TLS_README for details.
The Milter client now supports all Sendmail 8.14 Milter requests, including requests for rejected recipient addresses, and requests to replace the envelope sender address. See MILTER_README for details.
Postfix no longer adds (Resent-) From:, Date:, Message-ID: or To: headers to email messages with "remote" origins (these are origins that don't match $local_header_rewrite_clients). Adding such headers breaks DKIM signatures that explicitly cover non-present headers. For compatibility with existing logfile processing software, Postfix will log ``message-id=<>'' for email messages that have no Message-Id header.
Stress-adaptive behavior is now enabled by default. This allows the Postfix SMTP server to temporarily reduce time limits and error-count limits under conditions of overload, such as a malware attack or backscatter flood. See STRESS_README for details.
No functionality has been removed, but it is a good idea to review the RELEASE_NOTES file for the usual minor incompatibilities or limitations.
You can find Postfix version 2.6.0 at the mirrors listed at http://www.postfix.org/
The same code is also available as Postfix snapshot 2.7-20090511. Updated versions of Postfix version 2.5, 2.4 and perhaps 2.3 will be released with the same fixes that were already included with Postfix versions 2.6 and 2.7.