Today I installed the squirrel on my Thecus. The horde used before -- even if powerful -- was just to slow to make fun. As friends told me that the squirrel is slick and quick -- as its name suggests. (After installation, I can confirm this)
The squirrel -- is a web interface for accessing your mail, written in PHP. It does -- by default -- needs not to have any database. It can access your mail both by IMAP and by POP3.
As my setup is not the regular "Apache" based one, it might make sense to show how it has to be configured with lighttpd as web server.