On Technet Blogs  João Ribeiro published a nice high-level architecture overview of Exchange Server 2010. In the high-level architecture overview all roles like the Mailbox Server Role, the Client Access, Server Role, theUnified Messaging Server Role, theHub Transport Server Role and the Edge Transport Server Role are explained. Besides the Server Roles Management/Monitoring and High Availability methods are explained.

Download the poster here or go to the original post.