A single left click will display the message in the Message Pane if you have it turned on. Pressing F8 toggles the Message Pane on and off.

It takes a double left click to open a message in a window or tab.

Thanks for your effort; neither a single left-click nor a double left-click will open email that I have received. To read it, I have to right-click it and then open it in a new window. This occurred only 2 days ago, is quite vexing, and I hope someone can solve the problem. Many thanks for any help. Madison P.S. This problem pertains, also, to the icons on my desktop: same problem occurs !

MadisonEA said

P.S. This problem pertains, also, to the icons on my desktop: same problem occurs !

Time for a new mouse.