As much as I like the postfix/cyrus combo on OS X Server, it is not,
nor has it ever been, a good solution for someone hosting an ISP.
Don't know about Cyrus, but Postfix is CERTAINLY up for the job.
I use Courier IMAP on my home rig, and I love it, but.
At work (an ISP in Hawai`i), we use mailbox format...
so that means qpopper and UW-IMAP.
Again, I *HEART* Courier IMAP, and would commend it and Postfix
to handle this issue.
Use MacOS X (not Server) if necessary.
Aloha mai Nai`a!
--
"Please have your Internet License http://kapu.net/~mjwise/
and Usenet Registration handy..."