title: android: notify on gmail email with specific label income
body: <p>My app can send emails (<em>Gmail</em>) to other users.
  The problem is that I'd like to let the user know that the email he just received is from my app.
  I could do a notification service but I would prefer not as there are already tons of apps with running services and notifications.</p>
  
  <p>Is there a way to catch the incoming of a <em>gmail</em> email with a certain label or subject or from address ?</p>
  
  <p>I ask this because it looks so stupid to create another notification service when it's already there.</p>
  
  <p>edit: added <strong>gmail-api</strong> tag </p>