Wietse just released a quick update on the just released 2.4.2, it looks like the 2.4.2 release introduced a compiler bug on some platforms which was easily fixed. The bugs solved in this last release where:
Bugfix: don’t falsely report “lost connection from localhost[127.0.0.1]” when Postfix is being portscanned. Files: smtpd/smtpd_peer.c, qmqpd/qmqpd_peer.c.
Robustness: recommend a “0″ process limit for policy servers to avoid “connection refused” problems when the smtpd process limit exceeds the default process limit. File: proto/SMTPD_POLICY_README.html.
Safety: when IPv6 (or IPv4) is turned off, don’t treat an IPv6 (or IPv4) connection from e.g. inetd as if it comes from localhost[127.0.0.1]. Files: smtpd/smtpd_peer.c, qmqpd/qmqpd_peer.c.
Bugfix: Content-Transfer-Encoding: attribute values are case insensitive. File: src/cleanup/cleanup_message.c.
Bugfix: mailbox_transport(_maps) and fallback_transport(_maps) were broken when used with the error(8) or discard(8) transports. Cause: insufficient documentation. Files: error/error.c, discard/discard.c.
Bugfix (problem introduced Postfix 2.3): when DSN support was introduced it broke “agressive” recipient duplicate elimination with “enable_original_recipient = no”. File: cleanup/cleanup_out_recipient.c.
Bugfix (introduced Postfix 2.3): the sendmail/postdrop commands would hang when trying to submit a message larger than the per-message size limit. File: postdrop/postdrop.c.
Sabotage the saboteur who insists on breaking Postfix by adding gethostbyname() calls that cause maildir delivery to fail when the machine name is not found in /etc/hosts, or that cause Postfix processes to hang when the network is down.
Portability: Victor helpfully pointed out that change 20070425 broke on non-IPv6 systems. Files: smtpd/smtpd_peer.c, qmqpd/qmqpd_peer.c.
If you have no issues currently and all is working fine, there is no real need to upgrade. If it ain’t broke, don’t fix it.