I am not sure if we need to install ADC as part of 5.5 to 2003 migration (?) ADC populates and synchronizes user information between Exchange 5.5 and AD. Few months ago we had NT4 domain with PDC, and Exchange 5.5 DC. then we added Windows 2003 Server as a PDC, and removed the original (NT4) PDC. Now both of our DCs (Exchange 5.5 on Windows NT4 Server, and Windows 2003 Server) are fully synchronized ... Do we need to install the Active Directory Connector in order to add another Windows 2003 Server with Exchange 2003 (which will replace the existing Exchange 5.5)? Thank you.