I'm using Zimbra - but there are several now. Open-Xchange and two others we checked out (can't recall the names). All worked well had everything but Zimbra offered an API that matched a special project. We have an HP blade server (very heavy 150lbs) that no longer will have a windows server. Postgres for the database, Zimbra (postfix) for mail, Samba for file sharing, FTP , SVN, backup servers along with lots of little stuff, and general backup. So far all works well but there is talk of a data warehouse.

Johnf