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On a Microsoft Exchange Server 2007-based server, outbound queues stay at the "Active" status in Queue Viewer of the Exchange Management Console. At the same time, the message count of the queue is 20 or more. However, the messages to this destination (where the queue points to) are not delivered. Additionally, no non-delivery receipts (NDRs) are generated.
The Exchange server creates multiple connections for a queue whenever the number of messages in the queue exceeds 20. However, if the connection does not work, the queue does not enter a Retry state until the current connection count is decreased to zero. In a common situation, if the number of connections open is larger than one, and a transient error occurs, the queue stays active. When a new connection is created, the count never reaches zero. Therefore, the messages become stuck in the queue.
To resolve this problem, install Update Rollup 8 for Exchange 2007 Service Pack 1.
For more information about Update Rollup 8 for Exchange Server 2007 Service Pack 1, see the following Exchange Help topic: