Overview

When you think about it, message routing is concerned with three tasks:

1. Server to server message delivery
2. Location to location message delivery, where a location is a collection of servers
3. External message delivery

Exchange has always been good at routing. All Exchange 5.5 servers know about every other server in the organization and about every connector or available route that messages can take. This information is held in the DS and replicated along with all of the other configuration data. The MTA (Message Transfer Agent) takes this information and uses it to route messages quickly and effectively, and most of the time things work out very well. The wide range of connectors has helped to link Exchange to all of the other major messaging systems, including its main competitor, Lotus Notes, and many of the connectors handle directory synchronization. Exchange 4.0 through 5.5 certainly know how to route messages in all of the situations described above.

The goals for message routing in Exchange 2000 are as follows:

• Move to an SMTP-centric mode.l
• Exploit AD, DNS, and LDAP.
• Process messages at least twice as fast as the Exchange 5.5 Internet Mail Service, and be at least on a par with the SMTP service in MCIS (Microsoft Commercial Internet Server).

The old adage of "when something works, don't fix it" must have crossed the minds of the Exchange development team when the time came to decide how message routing should work in Exchange 2000. The temptation to leave well enough alone...