TABLE OF CONTENTS As a messaging system, the primary task for Exchange is to deliver messages in a reliable and robust manner. The Routing and Transport Engine is responsible for this work. Message routing encompasses three major tasks:
Server to server message delivery
Routing between different groups of servers
External and local message delivery
Exchange has always been good at routing and delivering messages. First-generation servers hold information about all of the other servers in the organization, including how the servers connect together in the Exchange Directory. The X.400-based Message Transfer Agent (MTA) uses this information to route messages quickly and effectively, and most of the time things work well. The wide range of available connectors helps Exchange to link up with its major competitors; many of the connectors also handle directory synchronization, which is of major assistance when you need to migrate from another email system. The combination of comprehensive connectivity and high-fidelity directory synchronization has been the cornerstone of Exchange s success in the enterprise messaging market. On the down side, when things go wrong with the MTA, administrators can tear their hair out to discover where the problem lies. Because of its age and the complexity of its code, Microsoft never upgraded the MTA to be a cluster-aware component.
Exchange 2000 and 2003 still support X.400, but the focus is now firmly on Internet protocols as the foundation for messaging with SMTP being the most important message transport protocol. As elsewhere in Exchange, the AD is the repository...
