For my entire career here at Microsoft I have been working with Messaging in some fashion.  Early on it was Key Management Server (KMS) for Exchange 5.5, I worked briefly on the Exchange SDK and then helped to make Mailbox manager a decent application, not just a tool, and then I branched off in to this group within Exchange called EPPU (Enhance Platform Product Unit), which eventually move to the Mobility team and became Microsoft Mobile Information Server (MMIS).  We shipped two versions of MMIS (2001 and 2002) in June 2001 and Dec 2001 (yes, 6 months apart).  MMIS was a middleware server product that gave mobile users wireless access to their Exchange data through Outlook Mobile Access and ActiveSync.  These are the same products that are now part of Exchange Server 2003.