Comment: Cyrus. (Score 1) 1216
Postfix + Cyrus IMAP and Cyrus POP3. Seperate your systems out (MTA v. Final Delivery). Use Cyrus Murder (as in a murder of ravens, or a cluster for us normal people.)
Back it up with LDAP for all the joyful goodness it bears (authentication, address books, etc.) If you want stronger authentication, add in Kerberos V.
I'm sure others will suggest all-in-one packages, but most of the ones I have seen are really some combination of Postfix or Sendmail combined with OpenLDAP and Cyrus, anyway.
Take your time to think about load-balancing, storage, and test, test, test!
It'll be a couple weeks of work (assuming you already have hardware and networking and storage gear), but you'll likely end up with a bulletproof mail system.
Back it up with LDAP for all the joyful goodness it bears (authentication, address books, etc.) If you want stronger authentication, add in Kerberos V.
I'm sure others will suggest all-in-one packages, but most of the ones I have seen are really some combination of Postfix or Sendmail combined with OpenLDAP and Cyrus, anyway.
Take your time to think about load-balancing, storage, and test, test, test!
It'll be a couple weeks of work (assuming you already have hardware and networking and storage gear), but you'll likely end up with a bulletproof mail system.