Dead-Letter Queues

Messages that have expired or are undeliverable are stored in dead-letter queues. A non-transactional message that cannot reach the destination application is stored in a dead-letter queue on the computer on which the message expired (or failed): this can be the source computer, the destination computer, or an MSMQ server that is forwarding the message.

Dead-letter queues are created for each independent client and server on your MSMQ network when MSMQ is installed on that computer. These queues are displayed under the computer in MSMQ Explorer.

Messages are undeliverable when:

The destination queue is unknown
The message has exceeded its maximum number of hops
The message time-to-be-delivered (TTBD) has expired
The message time-to-reach-queue (TTRQ) has expired
The queue's quota has been reached
A non-transactional message is sent to a transactional queue and the queue properties cannot be accessed when the message is sent

Messages are not stored in dead-letter queues when the message sender is not allowed to send messages to the destination queue. Messages in dead-letter and journal queues are always recoverable.

For more information on message properties (such as TTBD and TTRQ), see the MSMQ SDK. For more information on recoverable messages, see "Message Delivery" later in this chapter. For more information on queue and computer quotas, see "Queue and Computer Quotas" later in this chapter.