Directory Service Requirements for Exchange 2010

Component		Requirement
Schema master		The schema master must be running any of the following: Windows Server 2003 Standard Edition with Service Pack 1 (SP1) or later (32-bit or 64-bit) Windows Server 2003 Enterprise Edition with SP1 or later (32-bit or 64-bit) Windows Server 2008 Standard or Enterprise (32-bit or 64-bit) Windows Server 2008 R2 Standard or Enterprise
Global catalog server		In each Active Directory site where you plan to install Exchange 2010, you must have at least one global catalog server running any of the following: Windows Server 2003 Standard Edition with SP1 or later (32-bit or 64-bit) Windows Server 2003 Enterprise Edition with SP1 or later (32-bit or 64-bit) Windows Server 2008 Standard or Enterprise (32-bit or 64-bit) Windows Server 2008 R2 Standard or Enterprise
Domain controller		In each Active Directory site where you plan to install Exchange 2010, you must have at least one writeable domain controller running any of the following: Windows Server 2003 Standard Edition with SP1 or later (32-bit or 64-bit) Windows Server 2003 Enterprise Edition with SP1 or later (32-bit or 64-bit) Windows Server 2008 Standard or Enterprise (32-bit or 64-bit) Windows Server 2008 R2 Standard or Enterprise
Active Directory forest		Active Directory must be at Windows Server 2003 forest functionality mode or higher.