Best Web Based Email solution?

[Avatar <bshayn1@REMOVEME.umbc9.umbc.edu>]

I would like to install some sort of web based email solution for my
server. I definately want to stick with Apache as my web server and right
now I am using webmail (a real nice Perl script) as distributed by
opensource.jaos.org and it works fine, but I'm looking for something with
a few more features (address book, user accessable folders, the ability
to modify the html that people see, etc.).

I would like to stay in the realm of opensource and I am interested in
what packages other people have to recommend.