I don't know why you would be asking this question in this forum. That is probably why you didn't get much of a response. But if you are looking for an imap solution. Then you might want to look at Cyrus at
http://asg.web.cmu.edu/cyrus/.
If you are running anything sizable. It is know by people who have done large instalations of email that storing the email in a database is usually bad for performance. (on the scale of Hotmail, AOL, etc...)
Take a look at the postfix archives. (Found somewhere in www.postfix.org) There is a lot of good info on this buried there.
