On my old server, I was using Squirrelmail to host my own webmail.
I have since switched to a new VPS because the 192mb of RAM on the old one was not enough to host the site and the mail.
I reinstalled squirrelmail but in the end decided RoundCube looks a heck of a lot nicer and adds some functionality that I couldn’t get out of Squirrelmail.
Courier and Postfix round out the install to get my webmail running.
apt-get install courier-imap courier-imap-ssl postfix roundcube
ln -s /var/lib/roundcube /var/www/mail