title: How to find whether particular email id is a valid id or not before sign in that email service provider?
body: <p>I am creating a windows form where i get inputs for mail id,password,service provider name from the user...i want to validate whether the user entered email id is valid for the service provider entered in that form and send a file to google drive?. How to do it?. If i search i found <a href="https://developers.google.com/drive/quickstart-cs" rel="nofollow">this</a>  code but i don't understand it. or  any feasible solution is there?</p>