The Business Mail additional service improves the contact menu with two new functions:
1) Personal address books
2) Corporate address books
With the new Personal Address books option each email account can create various address books in your Webmail access, allowing all the users to order their contacts as they prefer.
Whereas the Corporate address book can only be managed by the Postmaster user, who can create and change the groups and contacts of this address book, which, however, can be displayed and used from each account of the domain.