Badge Count reflects all unread mail from your mail account(s), or just unread mail in your Focused Inbox. To learn more about Focused Inbox, please click here.
To disable/enable all badge count notifications, you can do this via the iOS Settings:
iOS Settings > scroll down to our app > tap Notifications > toggle on/off Badge App Icon.
To fine-tune what the badge count represents:
Open our app > tap Settings > scroll down and tap Badge Count > select All for all mail, or Focused Inbox for the badge to only represent the number of unread mail in your Focused Inbox.