Mail1Click offers an easy to use application program interface allowing to:
The API is based on XML, basically your application will call an https url with certain parameters and it will respond in xml. No encryption knowledge is required, because it is entirely delegated to the server's engine.
By Using the API you can develop a full email client or simply use it to send
encrypted email (ZERO TOLERANCY ON SPAM!!).
You can download the reference document from here.