title: how to check if a given email address actually exist in c#?
body: <p>I am building a C# application where users creat an account and type their email address,
  I know how to validate it with Regular expression, what I am having truble with is how to check if that email actually exist?
  i.e.   lilush@gmail.com  --> is there such email address?</p>
  
  <p>Thanks!</p>