In this example, Acme has three mail servers, Mail1, Mail2, and Mail3, each of which can route messages from the Acme organization destined for other Internet domains (external addresses). All three servers have the field "SMTP used when sending messages outside of the local Internet domain" enabled on the Router/SMTP-Basics tab of the Configuration Settings document that applies to them. One server, Mail2, receives mail addressed to the Acme Internet domain (acme.com). Mail2 has the SMTP listener task enabled on the Basics tab of its Server document.

If a user on one of the mail servers sends a message to an external address -- one with a domain other than acme.com -- the server looks up the destination domain in the DNS, connects to the destination server over TCP/IP, establishes an SMTP connection, and transfers the message.

Any mail from an external Internet domain -- one other than acme.com -- is routed to Mail2. The DNS lists Mail2 as the MX host for acme.com. Once the mail reaches Mail2, the server routes the message to its destination.

Since each server can send messages directly to external domains, no relay host, Foreign SMTP Domain documents, or SMTP Connection documents are needed.

Configuring these servers requires:

• Enabling "SMTP used when sending messages outside of the local Internet domain" for all three servers
• Enabling the SMTP listener task for Mail2
• Setting up DNS correctly to list Mail2 as the connecting server for the acme.com domain for inbound mail

Sample mail routing configurations

Glossary