Appointments in Outlook do not have invitees. In order to have invitees, the Appointment must be converted to a Meeting.
- Double-click on the appointment to open the appointment window.
- On the Appointment tab in the Attendees group, click the Invite Attendees button.
- Enter contact information for the people you want to invite to the meeting.
- Add a location if necessary, and then click the Send Invitation button.