Android GCM delivery monitoring

Question

I am developing mobile client for emailing service. One of the key features is notifications about new messages in the mailbox. As recommended by GCM architecture guidelines

Answer 1

Since that time Google has provided developers with advanced monitoring tool.

The Gcm Diagnostic Tool is available in Google Play developer console. Additional information is here https://support.google.com/googleplay/android-developer/answer/2663268

So you can easily track the particular message status via registration token.