What version of Outlook is your boss using? Frankly, without using search, there's no way for Outlook to know you suddenly want to sort by From when you're already sorted by date, just by you pressing a letter.

When I do it, in Outlook 2010, sorted by date, pressing the letters does nothing. If I Arrange by From then pressing the letters does exactly what you're asking for.

Now if I click in the Search field and start typing letters it certainly filters down the view to show me the senders with those letters.