Preview Pane – allows for simultaneous preview for part of an email while browsing/ replying to others. This is a very cool feature especially those who have OUTLOOK will be familiar with such kind of look.
Activating Preview Pane opens up a three-window panel for Gmail, with the Preview Pane in between the navigation and email panes. Activating the horizontal split places the preview pane at the top and emails below the preview pane. Users can change pane settings with a button that appears on the top right corner of Gmail.
One thing I notices is that Preview Pane is working only with Google Chrome (Web Browser by Google), which is little absurd but that is may be how Google can have more users for its web browser.
Preview Pane is part of Gmail Labs. This is Google’s newest Gmail Labs feature.