Microsoft KB Archive/251124

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XFOR: How to Configure Alias Table Functionality in Exchange Server

Article ID: 251124

Article Last Modified on 10/28/2006


  • Microsoft Exchange Server 5.5 Standard Edition

This article was previously published under Q251124


This article describes the difference in the way that Exchange Server and the UNIX Sendmail program route Internet e-mail mail messages, and provides steps to configure Exchange Server to use a connectivity structure that is similar to the alias tables that are offered by the UNIX Sendmail program. The steps in this article are not intended to replace common configuration concepts or guidelines, but to provide a workaround that implements a connectivity structure that is similar to alias tables.


In UNIX, the e-mail server program Sendmail can route incoming e-mail to various Simple Mail Transfer Protocol (SMTP) hosts by looking up the recipient's e-mail address and sending the e-mail message to the route that is defined in the alias table by the system administrator. Alias tables can also change the intended recipient's e-mail address before the e-mail message is relayed.

By default, the capability of Exchange Server to route e-mail messages by using e-mail addresses is limited, because Exchange Server can only route incoming e-mail by examining the recipient's domain name; it cannot route incoming e-mail by examining the entire e-mail address. Unless all of the servers are deployed in an Exchange Server-only topology with connectors, Exchange Server cannot leverage the message transfer agent to route e-mail messages by e-mail address.

For example, if inbound e-mail messages are sent to and and these recipients are homed on different servers that have no knowledge of each other, the relaying Exchange Server computer that is the entry point for cannot route the e-mail messages to the appropriate mailbox servers. Instead, the relaying server routes the e-mail messages to only one mailbox server, because Exchange Server has only domain name-to-server mapping, and this example requires a route defined by user name-to-server mapping, which is a feature of alias tables.

The following steps outline how to implement a connectivity structure that is similar to alias tables. After you perform these steps, Exchange Server can route e-mail by using the user name portion of e-mail addresses, and not just by using the domain name portion. The following procedure assumes that Exchange Server computers are the mailbox servers.

To configure an Exchange Server computer to route e-mail messages to mailbox servers:

  1. Create custom recipients (CRs) on the server that correspond to mailbox recipients on the mailbox servers. In the E-mail Addresses tab, make sure that each CR has the following properties:
    • An Internet-based address for directory lookup (for example, Set this address as the reply address.
    • An internal routing address to use for mailbox server-to-routing server relaying (for example,
  2. Click the General tab, and then modify the CRs domain-defined attribute (DDA) by clicking E-mail address. For the DDA address, type an internal routing address to designate a mailbox server (for example, After you perform these steps, Exchange Server changes the recipient's e-mail address to this newly defined DDA address before it sends a message, as the UNIX Sendmail program does.
  3. Click the Connections tab in the Internet Mail Service, and then click E-mail Domains. Add each internal routing subdomain (for example, along with the IP address or the fully qualified domain name of the corresponding mailbox server.
  4. Click the Routing tab of the Internet Mail Service, and then click to select the Reroute Incoming SMTP mail check box. To prevent unauthorized relaying, specify only the mailbox servers by clicking Routing Restrictions.

To configure each mailbox server to accept e-mail messages that are addressed to its internally routed recipients:

  1. Ensure that each mailbox recipient has at least the two following addresses:
    • A reply address of the primary domain name (for example,
    • A secondary proxy address that corresponds to the internal routing entry (for example,
  2. Click the Connections tab of the Internet Mail Service, click Forward all messages to the host, and then designate the routing Exchange Server computer.

If you want to use third-party messaging products instead of Exchange Server computers as the mailbox servers, make sure that the third-party messaging products are configured to send e-mail messages back to the routing Exchange Server computer, and to send outbound e-mail with a reply address that uses the original domain name (for example, Make sure that you enable the RerouteViaStore registry on the routing Exchange Server computer, in case UNIX servers or POP clients cannot change the reply address and need to relay messages back to the routing Exchange Server computer for e-mail message delivery to the Internet. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

238471 XIMS: How to Force SMTP Messages Through the Information Store

Additionally, you can use any domain name for internal routing, instead of the subdomain approach outlined in this procedure.

Any changes to the configuration of the Internet Mail Service require that you stop and restart the service.

Additional query words: "alias table" IMS

Keywords: kbhowto KB251124