When I originally wrote this post, Windows Server 2008 R2 Domain Controllers were not supported for Exchange 2003, however, in recent months the guidance from product team has changed and new support guidance now includes Windows Server 2008 R2 Domain Controllers as supported configuration.
Please refer to this article on Technet for more information.
MS Exchange Team recently published an article on Exchange 2007 Supportability Matrix. As I read more into it and look at the accompanying article on Technet, it is noteworthy that we talk about Exchange 2003 support as well.
I got questions from multiple customers I work with on this. As I realize many organizations are still in process of deploying Exchange 2007. Many have Exchange 2003 SP2 in production and majority of users are on Exchange 2003 mailbox servers.
This poses an interesting challenge. If an organization wants to move forward with Windows Server 2008 R2 (specifically – R2) Domain Controllers, they hit a huge roadblock. The supportability Matrix provides specific guidance around that and that means Exchange 2003 is not supported against Windows 2008 R2 Domain Controllers.
When I looked at Microsoft Support Lifecycle site for Exchange 2003, I noticed that Mainstream support for Exchange 2003 ended 4/14/2009. Given SP2 support note says support for SP2 will end at release of new Service Pack or end of Support Lifecycle of Exchange 2003 which is sometime in 2014, it still is important to note that when Mainstream support ends, only security fixes are provided for the product without any cost to customer.
It isn’t surprising that Exchange Product team may have decided to focus their efforts in developing features that customers asked for in current and future versions and not for the products that are in Extended Support phase of Lifecycle. I have no visibility in the effort of development and testing of any fix/service pack, features that goes into Exchange Server products but if I have to assume, I am sure it is huge for every possible combination they may have to test.
So to summarize, I know it is going to be painful to plan around the supportability of Exchange 2003 and Windows Server 2008 R2 Domain Controllers. The best approach I can recommend is follow the published guidance and plan around migration to Exchange 2007 before you can upgrade all your domain Controllers to Windows Server 2008 R2 and raise Domain / Forest functional level.
Last but not least, do read the site disclaimer, the views presented here are of my own and not of my employer.