Is it supported to install Exchange 2007 directly onto an EBS 2008 server? I have a client that has a single EBS server, and we would like to give them Exchange functionality without needing to purchase a separate OS license or server. They have 15 employees. So the route I am thinking of proposing is to buy Exchange 2010 Volume with CALS, and that should give them the right to use Exchange 2007, but do we need a separate OS? This then would also allow them to 'migrate' to Exchange 2010 when they get a new server (a few years out), and possibly to 2012, if we get these licenses with SA. They don't have large quantities of emails, so we don't need a separate server from a performance standpoint. It would only be a few GBs worth of email at this point, but they really need the features of Exchange, and they don't have alot of money to burn. I realize that they are 'supposed' to go with Hosted Exchange, however 1 year of hosting would basically pay for this, unless they need the additional OS. I found this which would seem to indicate it is supported: http://blogs.technet.com/b/essentialbusinessserver/archive/2009/08/25/how-to-install-exchange-2007-service-pack-2-on-windows-essential-business-server-2008.aspx However I don't see it listed officially in the OS section of the Exchange compatibility matrix: http://technet.microsoft.com/en-us/library/ff728623.aspx