What do the Sensitivity property's levels—Confidential, Personal, and Private—mean when applied to an appointment or meeting request?

Private is the only sensitivity setting that has any appointment-related functionality. Setting an appointment's or meeting request's Sensitivity property to Personal or Confidential has no effect. Perhaps that's why Outlook provides only a Private check box on the Appointment form and not a Sensitivity drop-down list like the one on a message's Options dialog box.

When you select an appointment's Private check box, you shield the appointment details (e.g., the meeting's subject, who you're meeting with) from everyone but a designated delegate of your mailbox. (To keep your delegate from knowing the details of a private appointment, open your mailbox's Tools, Options dialog box and go to the Delegates tab. Select the delegate and click Properties to open the Delegate Permissions dialog box, which Figure 1, page 8, shows, and clear the Delegate can see my private items check box.)

The appointment status appears when someone checks your availability, because the appointment date and time are included in your Calendar's free/busy information. However, people who have only Read access to your Calendar folder see the appointment subject as Private Appointment, as Figure 2 shows, and can't open the appointment.

The Private setting has no effect on meeting requests. Meeting request recipients must be able to see the meeting's date and subject. When you select the Private check box before sending a meeting request, Outlook marks as Private the appointment that it adds to each accepting recipient's Calendar folder.