I never liked Apple’s mail server, since it stores mail in a proprietary database rather than standard MBOX files, so I built and installed UW IMAPD.
It’s very easy: just download the source (currently at ftp://ftp.cac.washington.edu/imap/imap-2004.RC.tar.Z), unzip it, and build. I built it without SSL since it’s only accessible on my local network. If you want to do that, edit Makefile, look for the line ‘SSLTYPE=nopwd’ and change it to ‘SSLTYPE=unix’. It will warn you that it doesn’t meet the security standard, but you can tell it to go ahead. To build it, just type ‘make osx’.
After I moved the binaries to /usr/local/libexec, I went to server settings and disabled AppleMail, and then enabled imapd in /etc/inetd.conf.
I’m using it to archive all of my email on a local server instead of on my powerbook, as I was doing previously. I have it configured to use a Mail folder in my home directory, which I can back up easily.