title: Mailbox unavailable. The server response was: 5.7.1 Unable to relay for abc@xyz.com
body: <p>I am getting "<strong>Mailbox unavailable. The server response was: 5.7.1 Unable to relay for abc@xyz.com</strong>" when I try to send the mail using ASP.NET. The site is deployed on IIS7, Windows 2008 server.</p>
  
  <p><strong>The website was working fine on IIS6 and Windows 2003 Server</strong>. I deployed it on IIS7, 2008 it has started giving me this error.</p>
  
  <p>Has anybody experienced this before?</p>