The Amply API is organized around REST. Our API has predictable, resource-oriented URLs, and uses HTTP response codes to indicate API errors. We use built-in HTTP features, like HTTP authentication and HTTP verbs, which are understood by off-the-shelf HTTP clients. JSON is returned by all API responses, including errors.

The REST API has some advantages over SMTP:

If your ISP or hosting provider blocks traffic on mail ports.
If you do not control your hosting environment and cannot install/configure an SMTP library.

You can look at the full API documentation here.