Another cool Microsoft document updated: Front-End and Back-End Server Topology Guide for Microsoft Exchange Server 2003 and Exchange 2000 Server. Definitely a must read!
Microsoft Exchange Server 2003 and Microsoft Exchange 2000 Server support using a server architecture that distributes server tasks among front-end and back-end servers. In this architecture, a front-end server accepts requests from clients and passes them to the appropriate back-end server for processing. This guide discusses how Exchange Server 2003 and Exchange 2000 Server support the front-end and back-end server architecture. This guide also describes several front-end and back-end scenarios and provides recommendations for configuration.