> ## Documentation Index
> Fetch the complete documentation index at: https://docs.letterbucket.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Authentication

> Authenticate requests with a Bearer API key.

All requests require an API key in the `Authorization` header.

```
Authorization: Bearer sk_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
```

API keys are managed from newsletter settings → **API Keys**. The newsletter is resolved
directly from the API key.

<Warning>
  The API key scope is limited to the newsletter it was created for. A key cannot read or modify
  subscribers of another newsletter.
</Warning>