title: sending mail after payment paypal contact form 7
body: <p>I have a form with contact form 7 in a WordPress site. 
  When you click on "submit" you are redirected on Paypal and pleased to pay :). Everything works well, but the I want something more. 
  I want to send the mail, ONLY when visitors have pay on Paypal.
  I've searched on google, but I don't have found the way to do this.</p>
  
  <p>Any ideas ?</p>
  
  <p>Thanks !</p>
  
  <p>Nathan</p>