SummaryMultiple hosted exchange organizations on single Exchange server is called multi-tenant Exchange hosting. In multi-tenant exchange hosting the address books and organizations should be separated and hidden from each other. The article discusses how to achieve this.Following areas are covered in this article.Address List Segregation in multi-tenant exchange hosting environmentSecuring Address list - Hiding the email addresses from the GALMulti Tenant Hosting in Microsoft Exchange Server 2007Applies ToMachPanel all versionsMicrosoft Exchange 2007 SP1SolutionMachpanel only facilitates hosted email service provisioning and management on Microsoft Exchange 2007. There is separate service preparation procedure to prepare your active directory and Exchange server to host multiple organizations. The following Microsoft whitepaper describes shared hosting scenario where multiple companies are shared using the same Active Directory domain and can interoperate with each other. We recommend that you read and follow this white paper to properly secure your hosted exchange service:http://technet.microsoft.com/en-us/exchange/bb936719.aspxNote:The above solution may not be valid for HMC 4.0/MPS deployment. For more information about the Microsoft HMC solution, see: Microsoft Solution for Hosted Messaging and Collaboration version 4.0.