"Look at the Zimbra server. There is a free and paid version, the main difference being support."
Unfortunately, Zimbra is notavailable for Windows Home Server operating system. Zimbra Server is available for many popular operating systems: Red Hat Enterprise, Fedora, Ubuntu, Debian, Mandriva, and SUSE Linux plus Mac OS X, rPath (Software appliance ISO image), and VMware (certified virtual appliance). [Non-text portions of this message have been removed]
