We have added a new article in Microsoft Exchange Server section. The detail of this article is

Title: 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

Purpose: 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.

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