Add a "Flagged Email" folder in favourites
1. Go to Folder tab > New Search Folder
2. In the New Search Folder dialog box, click Mail flagged for follow up > click OK.
A new folder called "For Follow Up" will appear under Search Folders in the Navigation Pane.
3. Right-click the new folder > Add to Favorites
The "For Follow Up" folder will now appear under Favorites in your Outlook.