This is not a major issue but is another instance of a small change from Win 10.
NOTIFICATIONS – MAIL APP
As I have noted before, Notifications still appear on the right of the screen but, unlike Win 10, the icon (in the form of a blue circle with a number) only appears when there are notifications. The Mail App also shows unread Emails as a number on the icon in the Task Bar.
However, unlike Win 10, if you clear the Notifications, the unread Emails number also gets cleared from the Mail App icon in the Task Bar. (If you open the Mail App, the number of unread emails still appears on each Email Address.)
Just a small thing, but still something to be aware of if you use the Notifications to keep track of Emails.