Ha! I knew there had to be a keyboard shortcut. My boss (God bless 'er) just asked me if there was a way to expand all grouped items in a list in Outlook to save having to click on the little down arrow inside each group. And there is: right-clicking the little arrow and choosing Expand All Groups does the job for you.
But then I figured there had to be a keyboard shortcut somewhere for this. And through a process known as "brute force and ignorance" I discovered that pressing CTRL and the + key on the number pad does the same thing: Expand All Groups in the current view. And CTRL and the - key on the number pad does the opposite: Collapse All Groups.
Another mouse manoeuvre bites the dust!