Webhooks

Event: message.relayed

Sent when an outbound message is relayed through an upstream email provider and the provider assigns its own Message-ID. This is the push counterpart of GET /v1/messages/lookup: it gives you the original-id → provider-id mapping (one event per recipient) so you can correlate recipient replies (whose In-Reply-To references the provider id) back to the message you sent. Emitted only for mail that relays through an upstream provider; direct sends keep your original Message-ID and emit no event.

postWebhookmessage.relayed

Payload

idstring

Event ID (evt_...). Stable across retries — use it as an idempotency key.

object'event'

type'message.relayed'

Event type (e.g. message.relayed, test.ping)

api_versionstring

Payload schema version

createdstring date-time

When the event occurred (use this, not arrival order)

account_idstring

The account the event belongs to

Example payload

{
  "id": "evt_01J9XK4T8Q2M5N7P",
  "api_version": "2026-08"
}

Response

Return any 2xx status within 10 seconds to acknowledge the event.

Changes

Webhooks have no change history: a webhook is keyed by its event name rather than a path and method, so no recorded change can name it.