What e-mail header is needed for a message to be displayed as 'via:'?
<p>I have noticed that some mails come with the from address like :</p>

<blockquote>
  <p>Adam Mannet  via www.findyourfriend.com.</p>
</blockquote>

<p>What headers do I need to pass to the native PHP <code>mail()</code> function to accomplish this when sending e-mail? </p>
