Rather than a customer polling for status, a webhook pushes each delivery event (accepted, delivered, bounced, complained, opened, clicked) to a URL the customer registers, as soon as the event occurs.
Webhooks should be signed so the receiving endpoint can verify a payload actually originated from the platform and wasn't forged or replayed; signature verification typically also includes a timestamp tolerance window to reject stale or replayed deliveries.
A reliable webhook implementation retries failed deliveries with backoff and eventually dead-letters events the customer endpoint never acknowledges, so a customer's temporary outage doesn't silently lose delivery events.