Creating alarms for dead-letter queues using Amazon CloudWatch - Amazon Simple Queue Service
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Creating alarms for dead-letter queues using Amazon CloudWatch

You can set up a CloudWatch alarm to monitor messages sent to a dead-letter queue using the ApproximateNumberOfMessagesVisible metric. For detailed steps, refer to Creating CloudWatch alarms for Amazon SQS metrics. When the alarm notifies you that messages have moved to the dead-letter queue, you can poll the queue to review and retrieve those messages.