Outlook Unread Messages System Tray Envelope Icon Not Showing

The Outlook options structure is pretty arcane with all its n-levels of nesting. It’s pretty hard to find the option you want. So you had a envelope that shows you have unread mails before and it’s not there anymore. Bring it back with:

Tools -> Options -> Preferences -> E-mail Options -> Advanced E-mail Options -> Show an envelope icon in the notification area