Favorites can be turned off if you don’t use the feature and want more space to view the mail folder list in the folder pane. Favorites, located at the top of the Folder Pane, contain shortcuts to folders you frequently use.
No folders are added or removed when you turn on or off Favorites—it only changes whether the section appears in the Folder Pane. There is also no effect on folders in the main folder list.
In Mail, click View > Folder Pane > Favorites.
If you turn off Favorites, and then turn it back on, the same folders appear.