title: Clean unused tokens of Apple Push Notification on server-side
body: <p>I have my own server to implement Apple Push Notification. The implementation is:</p>
  
  <ul>
  <li>my server store APNS tokens of user in a table</li>
  <li>whenever there's a new pushing, it's retrieve tokens from that table, then push.</li>
  </ul>
  
  <p>Pushing is OK. But I have a confused issue: If the user turn off the APNS setting, how does my server know that, so it don't need to push to that token?</p>
  
  <p>Please help me. Thank you. </p>