I am looking at various FOSS options to build a robust EMail solution for a government funded university. Commercial options are to be chosen only in the worst case scenario. Here are the requirements:

• Approx 1000-1500 users - Postfix or Exim? (Sendmail is out;-))
• Mailing lists for different groups/Need web based archive - Mailman? Sympa?
• Centralised identity store - OpenLDAP? Fedora 389DS?
• Secure IMAP only - no POP3 required - Courier? Dovecot? Cyrus??
• Anti Spam - SpamAssasin? what else?
• Calendaring - ??
• webmail - good to have, not mandatory - needs to be very secure...so squirrelmail is out;-)?

Other questions:

• What mailbox storage format to use? where to store? database/file system?
• Simple and effective HA options? Is there a web proxy equivalent to squid in the mail server world? software load balancers?CARP?
• Monitoring and alert?
• Backup?

The govt wants to stimulate the local economy by buying hardware locally from whitebox vendors. Also local consultants and university students will do the integration. We looked at out-of-the-box integrated solutions like Axigen, Zimbra and GMail but each was ruled out in favour of a DIY approach in the hopes of full control over the data and avoiding vendor lockin - which i though was a smart thing to do. I wish more provincial governments in the developing world think of these sort of initiatives

As for OS - Debian, FreeBSD would be first preference. Commercial OS's need not apply. CentOS as second tier option...