I don't even use mail on my server; I figure, my own single server can't give me the type of redundancy that the Google Apps mail service can (and they even have a free service
here)...
So I don't even have to worry about keeping my spam lists up to date, or ssl certificates, or worry about making sure that imap/php3/smtp/spamassassin daemons aren't going out of control with process or memory usage...