A webhook endpoint returns 429 (Too Many Requests) for Event Grid event delivery. How does Event Grid respond?

1. A Drops the event immediately
2. ✓ B Treats 429 as a retry-able error and uses exponential backoff (correct answer)
3. C Routes the event to DLQ immediately
4. D Cancels the subscription

Shortcut: Event Grid treats 4xx errors (except 400, 413) and 5xx errors as delivery failures requiring retry. 429 triggers retry with exponential backoff, respecting the Retry-After header if present.