The Business Mail additional service has two more features in the Calendar menu:
1) Personal Calendars
2) Corporate Calendars
With the Personal Calendar each email account can create multiple Calendars within the same Webmail, allowing users to share their appointments/events.
The Corporate Calendar can only be managed by the Postmaster, who can create and change the events in the Calendar, which will be displayed and available to all the accounts of the domain with which the calendar will be shared.
The postmaster can enable other domain accounts to edit, create and delete events, using the "Share" function.