Mandatory absences are just that; enforced holidays for all users. This is great for catering for situations such as office closures over the Christmas period or where manufacturing customers have an annual factory shut down, for example.
If you have the 'Configuration Managers' role you will see the ‘Mandatory Absence’ option in the control panel via the configuration menu. Clicking on this option will give you the default absence plan upon which you can define Mandatory or Restricted dates. Select the applicable dates from the calendar and then select the option ‘Everyone has time off’.