XFOR: Applying Restrictive Address Spaces on the Internet Mail Service (229961)

SUMMARY

Using incorrect address spaces in the Internet Mail Service (Internet Mail Connector in Exchange Server 4.0) other than the default wildcard (*) entry can cause unexpected routing to occur with multiple Internet Mail Services configured. Non-delivery of outbound mail is also possible.

This article explains how to configure the Internet Mail Service properly, and why.

MORE INFORMATION

Message routing is performed by the Message Transfer Agent (MTA). The address space which best matches the recipient address is selected, based on the following preferences:

An exact string match: (for example, recipient = "SMTP:userz@microsoft.com" and address space = SMTP:userz@microsoft.com")
A wildcard string match: (for example, recipient = "SMTP:userz@microsoft.com" and address space = "SMTP:*@microsoft.com").

The wildcard string that matches more non-wild characters is given preference.
A partial string match: (for example, recipient = "SMTP:userz@microsoft.com" and address space = "SMTP:userz@com").
The address type matches and the address string is blank: (for example, recipient = "userz@microsoft.com" and address space = "SMTP:")

The MTA will evaluate the address and decide where to route it, and will do this by comparing the entire address of the recipient to the address space entered in the Internet Mail Service.

As the MTA does not work like a Domain Name System (DNS) resolver, it does not strip off the local portion of the address before matching it against the address space string. The whole user address is compared against the whole address space string.

A routing table entry of "SMTP:company.com" or "SMTP:@company.com" will not match a user of address "SMTP:user@company.com," whereas an entry of "SMTP:*@company.com" will match. The MTA will then choose a single connector from the set of connectors that support that address space.

As long as the Gateway Address Routing Table (GWART) doesn't change, the same address space will always be chosen during rerouting. Rerouting tries different connectors within the set of connectors supporting this address space.