MFCMapi makes it possible to edit the mailbox directly via the Messaging API (MAPI). This can be very usefull to remove a setting which is still on an object but is not visible anymore in the GUI. For example an user which is a delegate but does not exist in AD but you still receive error when trying to arrange a meeting with the mailbox. This can cause a lot of e-mails about non existing users. With MFCMapi you can remove the entry and solve the issue you have.