Installing Exchange 2003, 2007 in Exchange 2010 Org?
Bad news on all fronts for folks who plan on installing older versions of Exchange when the newest version already exists.
Q: Is it possible to install Exchange 2003 or 2007 in a pure Exchange 2010 organization?
A: If this is an Exchange 2010 greenfield environment (an Exchange organization that consists only of Exchange 2010 servers and never had previous versions of Exchange deployed), the answer is no. If you have transitioned from Exchange 2007 to Exchange 2010 and the last Exchange 2007 server has already been decommissioned, the answer is again no. You will not be able to install Exchange 2007 at a later time in this organization because it's now considered a pure Exchange 2010 organization.
If you plan to transition from Exchange 2003 to Exchange 2010 and you have already prepared the Active Directory forest using Exchange 2010 setup, again you can't install an Exchange 2007 server in the organization. You will, by the way, get a warning that mentions this when installing the first Exchange 2010 in a pure Exchange 2003 organization.
So if you think you'll need an Exchange 2007 server at some point, you should keep an Exchange 2007 server in the organization after transitioning from Exchange 2007 to Exchange 2010. Or, if you are transitioning from Exchange 2003 to Exchange 2010, you should deploy an Exchange 2007 server in the organization before you prepare the AD forest using Exchange 2010 setup.
[Editor's Note: This excerpt originally appeared in TechNet Magazine.]
Henrik Walther is a Microsoft Certified Master: Exchange 2007 and Exchange MVP with more than 15 years of experience in the IT business. He works as a technology architect for Trifork Infrastructure Consulting (a Microsoft Gold Certified Partner based in Denmark) and as a technical writer for Biblioso Corp. (a U.S.-based company that specializes in managed documentation and localization services).