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

# Authentication

> Authenticate to the Mailercloud API with an API key in the authorization header.

<Check>
  To authenticate, add an `authorization` header to your API request that contains an API key.
</Check>

API Keys allow you to use another method of authentication separate from your account username and password. API Keys add an additional layer of security for your account. To use keys, you must set a plain text header named `authorization` where the contents of the header is your API Secret Key.

```bash theme={null}
curl --request POST \
  --url https://cloudapi.mailercloud.com/v1/campaign \
  --header 'Authorization: Your API key here' \
  --header 'Content-Type: application/json'
```

<Warning>
  You are responsible for the security of your API key; we recommend that you store it in a secure location on your server. Because of the potential security risks associated with exposing your API key, Mailercloud does not support client-side implementation of the API using CORS requests.
</Warning>

## Creating API keys

Create your key directly here: **[app.mailercloud.com/account/api-integrations](https://app.mailercloud.com/account/api-integrations)** (in-app: Account → API Integrations). You can create up to 10 different API keys and delete a key whenever you want.

For the **Email Verifier API**, keys are separate — create them at **[app.mailercloud.com/email-verifier/api-keys](https://app.mailercloud.com/email-verifier/api-keys)** (in-app: Email Verification → API Key).