title: What does "Delivery to the following recipient failed permanently" mean
body: <p>What does the following error mean when trying to send <code>mail()</code> in PHP?</p>
  
  <blockquote>
    <p>Delivery to the following recipient failed permanently</p>
  </blockquote>
  
  <p>What are the causes etc. I notice that this happens when trying to send mail from the same domain. eg. website: example.com to email contact@example.com. If I try to send to test@gmail.com or even test@example2.com, it works</p>