White Paper: Configuring Virtual Organizations and Address List Segregation in Exchange 2007
This seems quite interesting when you have multiple companies using the same Exchange server.
View the White Paper here.
Summary
This white paper provides the information that you need in order to
configure Microsoft Exchange Server 2007 with multiple address lists so
different groups of users can have their own address list and secure
those address lists so that groups of users can only see their specific
address list.
Much of the information in this white paper originally appeared as individual Help topics in the Exchange Server 2007 Help.
In this white paper, we have consolidated the information that you need
to deploy and manage segregated address lists in one central location.
We have also provided sample scripts, which can be modified to fit your
environment, to help automate the provisioning of virtual organizations
and users.