Using New Outlook on Windows for personal email, calendar, and contact management
I HAD the same problem until I changed my "Favorites" list at the top of the navigation panel. I went to each of my 4 email addresses and clicked on the 3 dots to the right of INBOX for that email. Then I selected "Add to favorites" and the INBOX for that email appeared under Favorites. Then I went to Favorites and clicked on the 3 dots to the right of each of the default favorites I didn't want and selected "Remove from Favorites". Now in favorites, I have only my 4 email INBOXES With each email address in brackets alongside and when I get an email in that INBOX, it has a number to the right showing me that I have mail. I don't have to go to each email down below anymore to check for mail. It's not perfect but will do UNTIL MS gets a UNIFIED INBOX they should have had by now!
EDIT: You have to click on the email account to open the drop-down list of folders. I then selected my INBOX folder as the one I wanted in favorites. You can select any folder in the drop-down list by clicking the 3 dots and add to favorites.