Hi all, I am developing an Iphone Application which implements Apple Push Notification service (APNs). Everytime my application launch, it will send a device token to a server and store in a database in server. But if a user migrate to new device or reinstall operating system, the device token will change, and when run application, the application will launch again and send a new device token to server. But the previous device token it sent to server will become invalid (the device token sent to server before reinstall operating system will become invalid and no longer exist but still store in my database in server) ... Server (provider) will send notification to client based on the device tokens stored in database ... So, how can I check for those invalid device token? How can I check those device token which already not exist? This is because I need delete those invalid device token from database to prevent server send notification to them... Is it using "Enhanced Notification Format" to check for status code in error-response packet return by APNs when APNs finds an error? I need to do the checking of invalid device token in server side? or client side? Anyone have any ideas? Any suggestions and comments are welcome and appreciated. Thanks a lot.