title: Verifying an email address exist in C#
body: <p>Regarding <a href="https://stackoverflow.com/questions/565504/">this post</a>  about email verification,</p>
  
  <p>using C#, how would you</p>
  
  <ol>
      <li>issue a VRFY command</li>
      <li>issue a RCPT command</li>
  </ol>