Dead Letter Queues (DLQs) are a standard error handling mechanism for streaming software systems. In certain scenarios messages that cannot be processed by a production component when read from a queue are instead placed on a separate queue, the DLQ, for manual investigation and recovery. This ensures that subsequent messages on the original queue can continue to be processed, while any messages that cannot be processed are retained in full, i.e. there is no data loss.

Once a message has been placed on a DLQ this indicates that the standard processing of the message was not able to complete, and no further processing of the message will occur automatically. You must take additional steps in order to recover the original operation that was unable to complete. Failure to do so can lead to incomplete Vault functionality.