title: How to get the HTTP_REFERER from a Yahoo or Gmail
body: <p>I have an e-mailer script that send messages to Yahoo or Gmail with a link on it, a link that will return back to my website when it is clicked.</p>
  
  <p>I need to get the HTTP_REFERER from Yahoo or Gmail. in my site I have</p>
  
  <blockquote>
    <p>echo $_SERVER["HTTP_REFERER"];</p>
  </blockquote>
  
  <p>expecting something to return on it. but its empty.</p>