title: How to safely identify a DSN (delivery status notification) message
body: <p>I'm fetching emails from a POP3 server and I'd like to make a difference between a regular email and DSN (Delivery Status Notification) / NDR (Non-Delivery Report/Receipt) messages.</p>
  
  <p>What is the best/safest way to identify those messages? Are there any particular message-headers I should be looking for?</p>
  
  <p>Thanks in advance!</p>