Need a POP, IMAP, or web front for Exchange Server

/_Exchange!) Anyway, does anyone know of a product
/_out there (preferably open source) that can act
/_as this kind of front end for these Exchange
/_mailboxes?

IMP :-) Which is part of the Horde project if I am not mistaken.
It also has LDAP support, Addressbooks stored in MySQL, and more.
I used it, loved it, and found it to be rock solid.

-Mike