What is a dead letter queue (DLT) in Kafka?

A dead letter topic (DLT) receives messages that a consumer repeatedly fails to process. Instead of blocking the entire partition or retrying indefinitely, the consumer sends failed messages to the DLT after N retries and continues processing. The DLT pattern separates poison messages from the main processing flow. In Spring Kafka, DeadLetterPublishingRecoverer implements this automatically with the @RetryableTopic annotation. DLT messages typically include headers with error details for debugging.

Expected key concepts: dead letter topic, DLT, failed messages, retries, poison messages, DeadLetterPublishingRecoverer, RetryableTopic, headers, debugging