Microsoft Exchange is the Microsoft mail/collaboration/groupware system. It stores its data in a binary database, which makes things fun for disaster recovery.

Exchange provides standard IMAP, POP3, NNTP, and SMTP access, as well as the proprietary Exchange MAPI protocol. It also includes a webmail client (OWA, Outlook Web Access).

Ximian sell a connector for Evolution which uses OWA's DAV stuff to provide semi-native access to Exchange. Handy if the Exchange SysAdmin has disabled the internet protocols, or if you want to use Exchange's calandaring under Linux.

DBMail is a project to eventually build a open source Exchange workalike. In the meantime, there are several HOWTOs on the web describing how to implement similar services to Exchange (shared calandaring, resource management etc) on Linux.