Mail webhooks retry automatically, and you can send a test event
A Mail webhook delivery that fails is now retried for up to a day, every endpoint has a Send test, and the old single-slot webhook routes are deprecated with a sunset on 2027-01-15.
When your receiver is down or answers with an error, Mail now retries the delivery after 1 minute, 5 minutes, 30 minutes, 2 hours, 6 hours and 24 hours, with the same webhook-id every time so you can dedupe. Each event in GET …/webhooks/events shows when the next attempt is due. An endpoint that keeps failing (20 failures in a row, or a full day) is switched off; turn it back on with PATCH { "enabled": true }.
POST …/webhooks/endpoints/:id/test sends a signed example of any event type to the endpoint right away and returns what your receiver answered, so you can check your signature code before real mail goes out. The event log also filters by endpoint, status and time.
Deprecated: /webhooks/default and /webhooks/domains/:domain_id. They keep working, now with Deprecation and Sunset headers, and answer 410 after 2027-01-15. Endpoints created before today also keep receiving the older X-Mail-Signature header until then; new endpoints are signed with the Standard Webhooks headers only. See the webhooks guide.