I have some question want to ask. First is is it this code you provide is to validate email address exist at mail server or not? Second is this code is put at where? Is it put at after i double click email textbox at .cs file there ?
This code is for email validation. That means that it checks if email is correctly written, so if it is written in correct form only. Method returns true if all ok, and false if email is not in correct form.
You can call this method when ever you want.