You can edit or delete subkeys of the FilesNotToSnapshot registry key to include automatically excluded files in the backup. For example, to include OST files, do the following:
- Open Registry Editor (click the Start button, select Run, enter regedit in the Open: box and select OK).
- Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\BackupRestore\FilesNotToSnapshot registry key.
- Delete the OutlookOST value.
Keep in mind that the OST files exclusion is recommended by Microsoft. To learn more about the recommendation, see this Microsoft Tech Community article.