OSX MAIL的排版

今天我在外面無意看到別人的osx mail 竟然【功能欄】【信件欄】【內文】從左到右那樣排版！不像一開始default【內文】在【信件欄】的下面！要怎麼樣才能改成這樣啊！上面那樣講大家應該聽的懂吧！
看我的圖示吧
今天看到的:
___________________
|.......|...........|...............|
|.......|...........|...............|
|.......|...........|...............|
|.......|...........|...............|
|.......|...........|...............|
|.......|...........|...............|

原本的:
___________________
|............|......................|
|............|......................|
|............|___________|
|............|......................|
|............|......................|
|............|......................|


希望大家看得懂