The quickest way to create an all day event in the Microsoft Outlook calendar is to double-click in the space towards the top of the calendar. This opens up the Events dialog box.
However if you look in the Options group, you will see that the default in the Show As box is Free, whereas if you double-click at a calendar time to create an appointment the Show As box will indicate Busy.
There is no easy way round this except remembering to change the Show As box to Busy when creating an all day event.
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