An on-line version of this announcement is available at http://www.postfix.org/announcements/postfix-2.6.6.html
Postfix legacy releases 2.6.6, 2.5.10 and 2.4.14 contain fixes that were already included with Postfix 2.7 (stable release) and Postfix 2.8 (experimental release).
NOTE: Postfix 2.3 is no longer updated.
Defects fixed with Postfix 2.6.6 only (more in the next section):
"postmulti -p command" did not skip disabled instances.
In the multi_instance_wrapper parameter, the expansion of $command_directory and $daemon_directory was broken.
The address_verify_poll_count parameter value was not made stress-dependent by default. This defeated the purpose of making other settings stress-dependent by default with Postfix 2.6.
Defects fixed with Postfix 2.6.6, 2.5.10, 2.4.14:
Milter applications would hang up after receiving an unexpected SMFIC_HEADER (mail header) command. This problem happened with Milters that (legitimately) do not send replies for SMFIC_RCPT (recipient address) or SMFIC_DATA (start of message) commands.
Core dump while an printing error message for a malformed %<letter> sequence in LDAP, MySQL or PostgreSQL lookup table configuration.
Mail with zero recipients was forever stuck in the queue. This happened when "postsuper -r" was run after all the recipients of a message were delivered (or bounced), but before the message was deleted from the queue.
With hostnames such as 1-2-3-4, the valid_hostname() fuction did not recognize the '-' as a non-numeric character, causing a legitimate name to be rejected as "invalid".
The VRFY command did not accept a mailbox address inside <>.
The source code is available from ftp://ftp.porcupine.org/mirrors/postfix-release/index.html and from the mirrors listed at http://www.postfix.org/download.html.