Brief notes on upgrading from Postfix 2.3 to 2.6
================================================
(i.e. upgrading on Red Hat/CentOS 5.x)

Upgrading:
rpm -Uvh postfix-2.6.5-2.el5.i386.rpm postfix-perl-scripts-2.6.5-2.el5.i386.rpm

/usr/sbin/qshape is moved out to separate package, 'postfix-perl-scripts'.

main.cf will have new mandatory setting "data_directory";
  data_directory = /var/lib/postfix
will be added automatically on upgrade.
You would like to merge from main.cf.rpmnew, which will have 
surrounding comments.
Beware of existing SELinux which may be unaware of this path.

master.cf has new service: "proxywrite", "retry".
You MUST merge them from master.cf.rpmnew if your site modified master.cf.
(likely if SMTPs(465) and/or submission port (587) is enabled)
Unmodified master.cf will be silently upgraded.

Postfix 2.6 no longer adds missing Message-ID: header unconditionally.
Set "always_add_missing_headers = yes" for former behavior.

main.cf config "fallback_relay" should be updated to "smtp_fallback_relay"
which had been renamed since Postfix 2.2 but not in stock main.cf .
Old config still works.

Startup script /etc/rc.d/init.d/postfix is no longer considered a 
config file.
*.rpmnew and *.rpmsave will be generated on upgrade if you edited it.

(logwatch) Some maillog format had changed, causing daily logwatch(8) to
generate massive "Unmatched Entries". It may exceed message_size_limit 
on a busy mail server, resulting in no logwatch report.
Temporal solution:
Drop in a replacement, /etc/logwatch/scripts/services/postfix , which will
be run instead of stock /usr/share/logwatch/scripts/services/postfix .


See RELEASE_NOTES-2.* in the source distribution for details.
-- 
kabe.sra-tohoku.co.jp