I've had this problem in years gone by with older IE versions. They were fixed by doing things like dragging the corners out then hitting File > Exit etc.
That doesn't work with this - I'm using IE 11 and Windows 8.1. Most of the solutions I have come across this morning are for things like IE 10 and Windows 7 etc.
What I have tried to do so far
1. Drag edges of screen out then hit File > Exit. Has no effect, next time I open Outlook, it is still 1/2 screen.
2. Hold down Windows key and F11. Has no effect at all.
3. Hover over shortcut to Outlook, right-click then Properties. Supposed to show a Maximise button. Does not show.
4. Close every open screen, leaving only Outlook screen open, then drag edges out and hit File > Exit. Does not work.
I have gradually been replacing things I get Internet Explorer to do and shifting over to Chrome (beginning to despise IE more and more) but I am not sure how I can get Outlook to open with Chrome yet. That, of course, is a possibility which may solve this IE issue.
Does anyone know how to fix this current problem for IE 11 and Windows 8.1.? Older fixes appear to be of no use here.