To set this up, just follow the link below from Chrome and get that extension. You will then see a new app installed in Chrome and also a system tray icon too. To start Offline Gmail, just click on it from App Menu of Chrome or click on “Offline Google Mail” by right clicking on system tray icon.
On the first run you will be asked whether you allow to offline email or not. For your own safety, do not use this extension on a shared PC. If you are on your own PC, click on “Allow Offline Mail” and then hit continue.
Now you will be redirected to your Offline Gmail app. You can browse through your Email, search for one, give a mark on it or even compose one to send from this simple two pane app.