Is there any easy to install open source gratis MS-Exchange e-mail server replacement ?
It needs to be scalable, have IPV4+IPV6 support, include an SMTP server (including TLS), and a POP3/IMAP (IMAP 4 - push-IMAP) server, with LDAP/ActiveDirectory support, as well as a good spam and anti-virus filter, like ClamAV and SpamAssassin, and of course have no text-encoding problems (such as unicode support).
It also needs a Web-Interface, but WITHOUT using PHP (or anything that's worse when it comes to security than PHP, e.g. Apache).
It should run on Linux (and possibly Windows, too), store EVERYTHING (no external files except anything in /tmp such as for virus-scanning) in a relational database (e.g. PostgreSQL) and add as few external dependencies as possible.
It should also be scalable to a few hundred users at the very least.
Things I have investigated that don't cut it:
- Apache James (no webmail, IMAP search too slow)
- Dovecot (no integrated SMTP)
- Courier (good, but no database)
- Citadel (epic installation fail)
- Zimbra (very far from gratis)
- open-xchange (not gratis, not open source)