An advanced qmail distribution based on qmail-sql which has SMTP, SMTPS, POP3, POP3S, IMAP, IMAPS services, a content scanner, spoofing protections, SMTP AUTH support, SMTP-after-POP/IMAP, PHP5 API, SPF support and much more...
IMAP4 server working on top of SQL database (currently PostgreSQL but Oracle may work too). It has some unique features like elimination of duplicate messages throughout the whole system, possibility of clustering or load balancing etc.