
Firstly, make sure that you are using the latest version of Gmail. It should be version 4.2.1.
Launch the Gmail app and go to Settings > General Settings.
From this screen, check the box next to “Auto-fit messages”.
That’s all you need to do. Now you can return to your Inbox and see that emails will automatically fit your screen. This means that you will see a zoomed-out version of the email. If you want to zoom-in, then you can use the pinch gesture.
The previous version lacked this option which frustrated many users. This option, although not a major addition, it still makes more convenient to view emails on an Android device.
(Via: CNET)

