title: Best way to send notifications to an Android application
body: <p>I have a mobile application installed, say mail
  I have a web service/web application being hosted for intimating the mobile app whenever he gets a mail.
  Assume internet connection is ON in mobile.
  I just want to know if the mobile app would be monitoring the server web service frequently for the mail or the server web service would take care and send/trigger the pop up to mobile once gets the mail (without the need for mobile to monitor).
  Please assist and guide me to resolve this. Thanks in advance.</p>