I was reading the Google Developers documentation, and I was not able to find how to let GCM (Google Cloud Messaging) know to which device we want to send the message.
I am working on an application in which I'll be saving users' email addresses in my database. A user can invite another user to his group by specifying his email address. As soon as he enters the address of the person he wants to invite and presses submit, the request will go to GCM, which will notify the other user.
But how do I let GCM know to which mobile you have to send this notification?