Introduction
Understand general concepts, response codes, and authentication strategies.
Base URL
The Resend API is built on REST principles. We enforce HTTPS in every request to improve data security, integrity, and privacy. The API does not support HTTP.
All requests contain the following base URL:
Authentication
To authenticate you need to add an Authorization header with the contents of the header being Bearer re_123456789 where re_123456789 is your API Key.
Response codes
Resend uses standard HTTP codes to indicate the success or failure of your requests.
In general, 2xx HTTP codes correspond to success, 4xx codes are for user-related failures, and 5xx codes are for infrastructure issues.
| Status | Description |
|---|---|
200 | Successful request. |
400 | Check that the parameters were correct. |
401 | The API key used was missing. |
403 | The API key used was invalid. |
404 | The resource was not found. |
429 | The rate limit was exceeded. |
5xx | Indicates an error with Resend servers. |
Check Error Codes for a comprehensive breakdown of all possible API errors.
Rate limit
The response headers describe your current rate limit following every request in conformance with the IETF standard:
| Header name | Description |
|---|---|
ratelimit-limit | Maximum number of requests allowed within a window. |
ratelimit-remaining | How many requests you have left within the current window. |
ratelimit-reset | How many seconds until the limits are reset. |
retry-after | How many seconds you should wait before making a follow-up request. |
The default maximum rate limit is 2 requests per second. This number can be increased for trusted senders by request.
After that, you’ll hit the rate limit and receive a 429 response error code.
To prevent this, we recommend reducing the rate at which you request the API. This can be done by introducing a queue mechanism or reducing the number of concurrent requests per second. If you have specific requirements, contact support to request a rate increase.
FAQ
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