Migrating with Data...

It's one thing to upgrade software. It's an entirely different thing to migrate to new software. If you have a whole system of software, integrated in to a mega-app, it's even more difficult.

This, I knew, but actually executing is a real pain point. Here's our migration:

Old System:
Qmail + patches + smtpd
Courier IMAP, Courier POP3
Courier Authdaemon
Stunnel
Spamassassin
Vpopmail
Ezmlm
Mailman
Some DIY honeypot scripts
spamd greylisting
SQwebmail
Horde/IMP (which stopped working)
Qmailadmin

New System:
Postfix
Courier IMAP, POP3, Authdaemon maybe
Spamassassin
Mailman
Roundcube
As yet unknown www management tools

There's a lot of "fan in" or consolidation here. Postfix "does it all". All lists will become Mailman lists. The problem is transforming the data to fit into this new, simpler system. Simplifying your system isn't necessarily a simple task.