A very cool PHP and IMAP based web mail client. Check it out and their Wiki :-).
Notes on SquirrelMail
I like it when the front page shows the Unix /etc/motd file so I can get news bits and pieces out to those who don't have shell access. To do so do this:
Edit /usr/share/squirrelmail/login.php and add these lines after the closing </FORM>.
echo "<center><pre>\n"; readfile("/etc/motd"); echo "</pre></center>";