How to Use Mail Tabs in Mac OS
The Mac Mail app has gained tab support in the latest versions of Mac OS X, making it easier to juggle multiple emails on screen at once.
There’s a catch with using Mail Tabs in MacOS X, however, and that is you must be using full screen mode to gain access to the tab feature. Perhaps because of this, email tabs are particularly useful for laptop users with smaller screens, but this could also appeal to users who like to minimize distraction.