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Glossary · Published 2026-09-29 · AgentiSend team

Dead letter

Dead letter: A webhook delivery kept after the retries are used up, so it can be replayed.

A delivery that does not succeed is retried 10 times, on the schedule in the webhooks guide. After the last failure it is dead-lettered rather than dropped.

The console shows every attempt. Replay the dead letter once the endpoint is fixed. An endpoint that keeps failing is disabled and the account is notified. Verification of each delivery is webhook signing.

Related terms

  • Webhook signing — A timestamp and a signature over the raw body, checked before the payload is parsed.
  • Signature tolerance — How old a webhook timestamp may be before the delivery is rejected as a replay.