User Configuration > Administrative Templates > Microsoft Outlook 2016 > Disable Items in User Interface > Predefined
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\folders
This policy setting allows you to limit which permissions can be assigned to Default, Anonymous, or My Organization on mail folders and calendars. If you enable this policy setting, users can assign only the following permissions to Default, Anonymous, or My Organization. - None on mail folders - None or basic Free/Busy information on calendars Users won't be able to assign any other permissions to Default, Anonymous, or My Organization. All permissions will still be available to assign to other users on mail folders and calendars. If you disable or don't configure this policy setting, users can assign any permissions to Default, Anonymous, or My Organization on mail folders and calendars.