Favorites, located at the top of Navigation Pane, contains shortcuts to folders that you frequently use. Favorites is on by default, but can be turned off if you don’t use the feature and want more space to view the mail folder list in the Navigation Pane.
No folders are added or removed when you turn on or off Favorites — this only changes the display of the section in the Navigation Pane. There is also no effect on folders in the main folder list.
In Mail, on the View tab, in the Layout group, click Navigation Pane, and then click Favorites.
If you turn off Favorites, and then turn it back on, the same folders appear.
Tip: If the Favorites command in missing, you are probably in Folder List, not Mail. In the Navigation Pane, click Mail.