title: Mailbox unavailable. The server response was: 5.7.1 Invalid credentials for relay
body: <p>At our office others can use the .NET SMTP client to send email via our Google Apps account.  Using the exact same settings and credentials this does not work on a particular machine.  It seems to be just this one machine with this issue.  I get:</p>
  
  <pre><code>Mailbox unavailable. The server response was: 5.7.1 Invalid credentials for relay
  </code></pre>
  
  <p>We are all on the same external IP, so it's not</p>