ArjanS wrote:

When i create an appointment in the calendar of my boss, he receives
an email with the appointment, but it is not displayed as tentative
in his calendar (never).
With the calendar of other collegues it works fine. They also receive
the email with the appointment and it is directly shown as tentative
in their calendars.

Are you his delegate? Perhaps you have permission, then, to add items to
his calendar.
--
Brian Tillman