Exchange 2000 was an amazing update to the product. The directoryn containing the list of mailboxes, recipients, etc. moved to Active Directory, and SMTP became the primary protocol used to communicate, both withing Exchange and betwen Exchange and other message systems, Significant improvements to OWA were Microsoft's first attempt at making it a viable primary client (although in my experiance, it wasn't until Exchange 2003 that OWA was really looked at as real messaging client). Exchange 2000 continued to support the chat serivce. but also had new instant messaging (IM) service that has since moved out of Exchange into Live Communication Server. Exchange 2000 was supposed to be the "anytime, anywhere, any client" messaging platform, but beyong OWA, Outlook 2000, and any standard POP3/IMAP4 client.
