XFOR: How to Configure Exchange to Share SMTP Domain Name Space

This article describes how to configure Exchange Server 5.5 to share Simple Mail Transfer Protocol (SMTP) domain name space.

Exchange Server 5.5 can be configured to share SMTP domain name space by configuring the Internet Mail Service E-mail Domain option. When you set this option, organizations with disparate mail handling systems are able to use a single SMTP domain. With this method, organizations are limited to sharing the name space with a single mail server. A SMTP custom recipient must be configured for every recipient in a different mail system.

When mail is received by the Internet Mail Service, the service queries the Exchange Server 5.5 directory for the target recipient. When the target recipient is not local to the Exchange-based server, messages are rerouted to the mail server that is specified in the Internet Mail Service E-mail Domain option.

If a custom recipient for the remote user does not exist, the message is returned as non-deliverable.

In cases where Exchange Server synchronizes directories with a foreign mail system, you must remove the SMTP proxy address from the custom recipient that is associated with the foreign system address type, for example, Lotus Notes.

To configure the E-mail Domain option, follow these steps:

1. Make an SMTP custom recipient for the user in the other mail system.
2. Double-click the Internet Mail Service, and then click the Connections tab.
3. Click E-mail Domain and click Add.
4. Type the shared SMTP domain name in the E-mail Domain box.
5. Click the Forward all messages for this domain to host check box and type the Fully Qualified Domain Name (FQDN) or Internet Protocol (IP) address of the SMTP mailer for the other system.
6. On the Routing tab, click Add, on E-mail sent to this domain:, add the new shared domain name, click to select Should be accecpted as inbound, and then click OK. The new domain name should allow the IMS to accept mail.
7. Restart the Internet Mail Service.