- Close Outlook
- Download MFCMAPI from http://mfcmapi.codeplex.com/
- Run it
- Login to MAPI with it
- Double-click the folder for your mailbox (e.g. “Lastname, Firstname” in a corporate environment)
- Expand the Root item
- Look in IPM_SUBTREE
- Select the desired folder
- From the menu: Property » Advanced » Edit
- In Property Tag type; 0x10F4000B
- Press OK
- Put a check-mark in front of Boolean
- OK/close your way out of all windows