I went through the push notification doc provided by gmail,but I am confused, I got the idea of creating topic and publishing the message to that topic but my problem is if I send email if any reply comes on that thread than how should get on my we webserver I can check the thread by sending api call,but I need to send the api call at some time so I want push notification but after going through doc ibwas confused in watch method we are giving user id but if the user is not subscribed to that topic than wat would happen