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The POST /v1/inboxes/{id}/send endpoint requires an Idempotency-Key header. If you retry with the same key, we return the original response without sending a duplicate email.

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Usage

curl -X POST https://api.openmail.sh/v1/inboxes/inb_xxx/send \
  -H "Authorization: Bearer om_live_..." \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000" \
  -d '{"to": "user@example.com", "subject": "Hello", "body": "Hi"}'

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Rules

  • Unique per send — Generate a new UUID for each distinct send (e.g. uuidgen, crypto.randomUUID()).
  • Scoped to account — Keys are per-account, not global.
  • 24-hour expiry — Keys expire after 24 hours. Reusing an expired key creates a new send.
  • Same body — Retries must use the same request body. Changing the body with the same key returns an error.

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Webhook idempotency

For webhooks, use event_id to deduplicate. We may deliver the same event more than once; your handler should be idempotent.