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In an Exchange Server 2003 and Exchange Server 2007 coexist environment, you create a Non-MAPI public folder on Exchange Server 2003 and enable the mail feature for the public folder. However, when an Exchange 2007 user sends a message to the mail enabled Non-MAPI public folder, the message stays in the "Unreachable Domain" queue on the Exchange 2007 Hub Transport server. If you check the message in Exchange Management Console by using the Queue Viewer tool, the Last Error column shows the following error:
There is currently no route to the mailbox database.
Eventually, the user receives the following non-deliver report (NDR) message:
#550 4.4.7 QUEUE. Expired; message expired in unreachable destination queue. Reason: There is currently no route to the mailbox database ##
This issue occurs because Exchange Server 2007 does not support to route a message to the mail enabled non-MAPI public folders.
To resolve this problem, install Update Rollup 7 for Exchange 2007 Service Pack 1. For more information about Update Rollup 7 for Exchange Server 2007 Service Pack 1, see the following Exchange Help topic: