MailEnable Enterprise Edition has the option to select contacts from a Global Address List. Global Address Lists are configured by the manager or server operator.  The Global Address list can be seen by all of the mailboxes within the post office that it is configured for.

The selection of contacts in this list is the same as the personal contact address book except that the selection box on the top right hand side has “Global Address List” Selected (as shown below circled in orange).  You can swap between both personal contact lists and the Global Address List by clicking on this combo box.