In message queueing the dead letter queue is a service implementation to store messages that meet one or more of the following criteria :
- Message that is sent to a queue that does not exist. 
- Queue length limit exceeded.
- Message length limit exceeded.
- Message is rejected by another queue exchange.
- Message reaches a threshold read counter number, because it is not consumed. Sometimes this is called a "back out queue".
Dead letter queue storing of these messages allows developers to look for common patterns and potential software problems.
Queueing systems that incorporate dead letter queues include Amazon Simple Queue Service  , Apache ActiveMQ, HornetQ, Microsoft Message Queuing  ,WebSphere MQ  and Rabbit MQ  .