> ## Documentation Index
> Fetch the complete documentation index at: https://openmail-docs-reputation-lifecycle-webhooks.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Idempotency

> Use idempotency keys to safely retry failed send requests without creating duplicate emails. OpenMail rejects duplicate requests for 24 hours.

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.

## Usage

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

## 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.

## Webhook idempotency

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