Why does opening Mac Mail show a preview pane not the whole email? On my MacBook OS X 10.10.3 when I used to open Mac Mail it would just display the entire message and there was more flexibility to deal with this or other messages. Now it seems to load a preview (constrained) version of the message with fewer options not the entire message as before. Looking on viewing preferences there is no obvious way to view email messages as before.
Quickest way to get the old view back is enable Classic Layout, prefs > viewing...