emails in Inbox will not open in full screen

 when I open a received email it opens in a smaller window attached to the top right of the screen and can only be closed by clicking the X from the task bar.  This is something recent but I cannot find how to fix it.

just maximize the window and close the open email, all subsequent email should open full window

Thank you Buddy and I would have done that but that’s the problem there is no minimise, maximise button showing - it’s like part of the bar is missing and a smaller window is stuck to the top the screen - I can’t drag it away from the corner, and not scroll bar down the right hand side either. 

I will see if I can duplicate when I get home.