I received a lot of junk mail today and, in order to try to move it all in one move, I dragged the message pane downwards so I could select all the unwanted messages. However, I seem to have removed the lower pane to view the currently selected message. All I see is the list of messages but I can only read them if I double-click each message so that it opens in a separate window. How do I restore the Mail window so that I can see the list of messages in the top half and the selected email content in the lower half? I tried to drag the little dot at the bottom of the window but nothing happens.