voodootikigod/postmark.js — pull request #16 by trupin (2013-06-12 15:47:00+00:00)
Title: Manage the case where a non-JSON format is resturned by the API

The JSON.parse error is caught and the message "Unsupported Request Method and Protocol" is now returned.

In my case I got the error "Unsupported Request Method and Protocol" placed into an HTML page. So I fixed it that way, but it could occur because of an other kind of error.