title: SQS Lambda - Redrive Policy vs DeadLetterConfig
body: <p>I have set up lambda integration to SQS with fixed reserved concurrency to throttle requests to a backend service. I need to use a DLQ to track and store errors.</p>
  <p>What are the differences in behavior between using the Redrive Policy of the SQS vs the DeadLetterConfig of the lambda function?</p>
  <p>I am particularly interested in the behavior when there are huge amounts of messages in the Queue but with limited lambda concurrency.</p>