Postfix snapshot 20090123 provides support for managing multiple Postfix instances. It was designed, implemented and documented during this week (implementation taking about 1/6 of that time).
Citing from the RELEASE_NOTES: This can automatically apply your "postfix start" etc. command to multiple Postfix instances, including upgrades to new Postfix versions. Multi-instance support allows you to do the following and more: - Simplify post-queue content filter configuration by using separate Postfix instances before and after the filter. This simplifies trouble shooting and performance tuning. - Implement per-user content filters (or no filter) via transport map lookups instead of content_filter settings. Mail for some users can be sent directly from the before-filter instance to the after-filter instance. - Test new configuration settings (on a different server IP address or TCP port) without disturbing production instances. - Each additional Postfix instance uses a few files and directories, plus memory for an extra master daemon and queue manager. The pickup daemon is needed only if you use local submission or "postsuper -r". Best of all, nothing changes when you use only one Postfix instance. The postfix-wrapper script (in the daemon directory) implements a simple but useful multi-instance manager, with instructions. The plug-in API itself is described in the postfix-wrapper(5) manpage. A more sophisticated multi-instance manager called postmulti(1) is approaching completion. A prototype version has been used internally at Morgan Stanley. This version will be adapted to the new plug-in API which makes some simplification possible. Wietse