I have a fully functional Postfix server running Apache and MySQL.
As RoundCube’s webmail requires IMAP, I also installed the Dovecot IMAP server from the OpenBSD ports tree. Then, I unzipped RoundCube’s webmail package to my webroot, and in 5 minutes it was running and working properly on an OpenBSD-3.8-STABLE server. Check it out at RoundCube’s website.
This is a must-have webmail interface. (even tho it’s kinda RedHat-ish, I still like it!)
Plus, it’s completely skinnable with XHTML and CSS2.