What is a DLQ, and how do you return to failed messages?

A DLQ, or dead-letter queue, is a separate queue for messages that couldn't be processed correctly under the agreed rules. With it, one permanently failing item doesn't circulate endlessly in normal traffic. But someone has to notice the problem and fix it.

Before resending, I check the cause of the error, whether the data is still current, and whether the effect has already been saved. I replay gradually and keep the original operation's identifier. If I give every attempt a new ID, I can bypass my own duplicate protection. Alarms, retention and someone responsible for handling it matter — not just creating the DLQ.