title: Is sending an email to username@facebook.com an allowed means of contact?
body: <p>I've noticed that I can send email to <code>username@facebook.com</code> and it will get delivered to a user's Facebook inbox. Is this allowed to be done programmatically (eg send via SendGrid to re-engage users)?</p>
  
  <p>Does anyone have any experience doing this? If it's allowed is there anything to watch out for or be aware of?</p>