- Dead-letter queue is used to send undeliverable messages to a dead-letter queue. Sometimes, for example, if there’s a bug in the worker… — - Once we’ve found the problem in the worker, fixed the bug and deployed a new version, we want to send all the messages from the DLQ back to the original input queue, so they can be processed by the updated worker. There’s no way to do this in SQS directly, so we’ve written a script to do it for us.