Processing messages on an IBM MQ dead-letter queue

To process messages on a dead-letter queue (DLQ), IBM MQ supplies a default DLQ handler. The handler matches messages on the DLQ against entries in a rules table that you define.

Messages can be put on a DLQ by queue managers, message channel agents (MCAs), and applications. All messages on the DLQ must be prefixed with a dead-letter header structure, MQDLH. Messages put on the DLQ by a queue manager or a message channel agent always have this header; applications putting messages on the DLQ must supply this header. The Reason field of the MQDLH structure contains a reason code that identifies why the message is on the DLQ.

All IBM MQ environments need a routine to process messages on the DLQ regularly. IBM MQ supplies a default routine, called the dead-letter queue handler (the DLQ handler), which you invoke using the runmqdlq command.

Instructions for processing messages on the DLQ are supplied to the DLQ handler by means of a user-written rules table. That is, the DLQ handler matches messages on the DLQ against entries in the rules table; when a DLQ message matches an entry in the rules table, the DLQ handler performs the action associated with that entry.