E-mail messages that are bound for an Exchange Server 2003 server that is not in the same site may sit in an Exchange Server 5.5 message transfer agent queue

Consider the following scenario. You move mailboxes from a server that is running Microsoft Exchange Server 5.5 to a server that is running Microsoft Exchange Server 2003 on another site. Then, you try to send an e-mail message to a migrated user. When you take these actions, the e-mail message that you try to send may route to a Message Transfer Agent (MTA) queue in the server that is running Exchange Server 5.5. You may also receive a non-delivery report (NDR) message. This problem occurs even though no route is configured.

This problem occurs when the e-mail message is resolved to a hidden object on the server that is running Exchange Server 5.5. This hidden object has the server name of the original server that is running Exchange Server 5.5 Server instead of the server name of the server that is running Exchange Server 2003.

Therefore, the e-mail message is queued in the MTA queue whose destination is the server that is running Exchange Server 2003. To the server that is running Exchange Server 5.5, the server that is running Exchange Server 2003 appears to be a local server within its site.

The root cause of this behavior is that the hidden object still has membership to one or more groups. If you try to resolve the name in the e-mail message, the following information may appear:

To resolve this problem, make sure that all Exchange Server 5.5 groups are synchronized to the Active Directory directory service. To do this, use the Active Directory Connector (ADC) in Exchange Server 2003.

This behavior is by design.