Invitation delivery callbacks

This page is for operators integrating an email provider's delivery callbacks.

OpenPost separates email provider acceptance from confirmed delivery. A successful delivery job marks a Workspace invitation Sent. It means the provider accepted the request. It does not prove delivery. A verified callback can later mark that exact delivery Delivered or Delivery failed.

Set OPENPOST_EMAIL_DELIVERY_WEBHOOK_SECRET and send callbacks to POST /api/v1/email/delivery/webhook. Sign the exact request body with HMAC-SHA256 and send the lowercase hexadecimal digest as OpenPost-Signature: v1=<digest>.

json

{
  "event_id": "provider-event-unique-id",
  "invitation_id": "OpenPost invitation ID",
  "delivery_id": "OpenPost email delivery job ID",
  "outcome": "delivered",
  "occurred_at": "2026-08-14T12:01:00Z"
}

outcome is delivered or failed. event_id must be stable across provider retries. OpenPost records only these identifiers, the outcome, and timestamps. It does not store the callback body, recipient address, provider response, or invitation secret in callback evidence.

Duplicate event IDs return success without applying the event again. OpenPost ignores callbacks for an older resend generation, an accepted or revoked invitation, or an outcome older than the current callback state. Unknown invitation IDs also return a successful ignored result so the endpoint does not become an invitation lookup surface.

Invitation delivery callbacks ​

Invitation delivery callbacks