Server administrators be warned; if you’re looking at Windows Server 2008 R2 you need to be aware it is not currently supporting Microsoft Exchange 2007 on this platform. Instead, you must upgrade to Exchange 2010.
This news was made public via the Microsoft Exchange Team blog when discussing rollup 9 for Exchange Server 2007 service pack 1.
Specifically, the Exchange Team note that one of the fixes in the RU is “Support for Windows Server 2008 R2 Domain Controllers in the environment” adding the disclaimer “Note: Exchange Server 2007 itself is not supported to be installed on a Windows Server 2008 R2 system.”