We have recently acquired an old company where we have 3 Windows 2003 Domain Controllers where AD +Exchange 2007 SP1 is installed on the same server. I would like to perform transition to Windows 2008 R2, which is fairly easy.
The Windows 2003 domain Functional Level is Windows 2003
Forest Functional Level is Windows 2000.
I have read the below article with regards to Exchange 2007 SP1 against Windows 2008 R2 Active Directory.
Exchange Server 2007 is not supported on Windows Server 2008 R2. However, Exchange 2007 SP1 RU9 and SP2 are supported against Windows Server 2008 R2 Active Directory servers. In addition, Exchange 2007 SP1 RU9 and SP2 are supported in Active Directory environments whose domain/forest functional levels have been raised to Windows Server 2008 R2.
If I am not wrong the above lines quoted in bold lines means that I can use the same forest functional Levels and Domain Level as it is and also later If I am upgrading it to Windows 200R2 (Functional Level and Domain Level) it will work.