AngularJS email validation using Mailgun's free API (http://blog.mailgun.com/post/free-email-validation-api-for-web-forms/)
Usage:
<input type="email" ng-model="email" guardpost-check>
<!-- ... -->
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.0.1/angular.js"></script>
<script src="angular_guardpost.js"></script>
<script>
guardpost.value("mailgunKey", "YOUR_API_KEY");
</script>