With the release of Exchange 2007 SP2 we provided a Supportability Matrix which outlined the supported configurations for Exchange 2000 SP3, Exchange 2003 SP2, and Exchange 2007 (RTM, SP1, and SP2)...
Updated Jul 01, 2019
Version 2.0
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One last thing, the Exchange 2007 installation added the new "Exchange Administrative Group" and the new server to the Exchange Management Console on our existing Exchange 2003 org. Do you have any documentation on removing Exchange 2007 from an Exchange 2003 organization so that I can do the uninstall and reinstall?
It is a shame that when the Exchange 2007 install checks the prerequisites and even downloads the new prereqs before installing, it doesn't notice that 2008 R2 is installed and instead allows the install to continue.