Google Labs may be phasing out, but that doesn’t mean new features have to stop rolling out right this minute. If you are longing for the new Mail app in OS X Lion, but are waiting for some bugs to be ironed out, or, if you just happen to like a dual-pane message view, open Gmail and go to Settings, Labs. Under that heading, you’ll find an option for “Preview Pane.”
Enable it and save, then return to your inbox. On the right side, you’ll see a new layout button that allows for vertical and horizontal splits. Selecting either one separates your message list view from individual email view, so you don’t have to click back: just tap a message in the list and it appears in the new pane.
Via All We Like