title: Mailbox unavailable error
body: <p>When trying to send out an email in a .NET site, the following error is being encountered:</p>
  
  <pre><code>Mailbox unavailable. The server response was: No such user here
  </code></pre>
  
  <p>Does this error appear if the code is trying to send to an email address which doesn't exist?</p>
  
  <p>Thanks.</p>
  
  <p>I now have more information about this error. The emails are sent from 'noreply@[domain]'. When the emails are sent to an email address of the same domain, the emails are sent without a problem. This error only appears when the email addresses being sent to are not from the same domain. I don't know if that's any use?</p>