XFOR: Internet Mail Service May Relay Messages Despite Restrictions

The Exchange Server 5.5 Internet Mail Service may relay messages if the messages are sent to a specific encapsulated addressing format.

This issue can occur if the message is sent to a server that is using one domain (for example, domain1) that is set to forward all messages to another domain (for example, domain2). The forward all messages option is set on the Connections tab. The server is also configured to reroute inbound SMTP mail (set on the Routing tab), has the routing restriction for Hosts and clients that successfully authenticate selected, and is configured to accept mail from "localdomain.com". The message is in the following format: This format implies that this user does exist on domain2 and that domain1 has site addressing set to localdomain1.com.

To resolve this problem, obtain the latest service pack for Exchange Server 5.5. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in Microsoft Exchange Server version 5.5. This problem was first corrected in Exchange Server 5.5 Service Pack 4.