Not Cyrus IMAP, but their SASL library. Actually, I just looked. Cyrus-sasl was pulled in as a dependency for mutt. I'm using Dovecot for postfix's SASL backend these days. This allows relaying mail for authenticated users only.
Dovecot uses PAM for authentication, and so any user with an account can log in and access their own mailbox and send mail out. The biggest downside is that because I'm deviating from the default FreeBSD configuration for postfix I'm on my own in terms of updates.
I should also clarify the above statement about moving it all into a jail -- I mean a jail managed by (in this case) ansible. Yes, if you just slap something together it will be brittle no matter what stack you choose. Ansible + Jenkins + Jails make it much easier to manage changes.
Edit: Oh yeah, and I've thrown procmail in there for good measure.
