In case you don't know by now, the Windows 10 Mail app is fantastic, and becomes even moreso today with a new update. One of the key changes is one click switching between accounts. Before you would, annoyingly, be required to make two (doesn't get much more "first world problems" than that, huh?), but those days are over now.
Next is more personalisation options, allowing you to customize colours in the left pane and for email selection (you can pre-select from a list or add an image of your own to draw from), as well as switch between the previous light theme and a new dark theme.
It's possible other changes are hiding beneath the surface as well.