I have a Domain Controller that is Win 2003 R2, it used to be Win 2000. I also have several Win 2008 R2 Domain controllers that were recently added. The mail server is Exchange 2003 R2 running on Windows 2003 R2. I checked and the Domain Functional Level is Windows 2003 but the Forest Functional Level is still Windows 2000. At some point I want to get rid of the Win 2003 Domain controller (it currently has all the FSMO roles), thereby making all Domain controllers Windows 2008 R2. Would there be any impact to Exchange 2003 if I raised the Forest Functional level up to Windows 2003? What about Windows 2008?

Hi, As long as you have a Domain Controller that is W2K3, you can't raise the domain and forest functional level to Windows Server 2008. Raising the forest up Windows Server 2003 FL, is something you should do and it will not impact Exchange in a negative way. Exchange 2003 also has support for Windows Server 2008 forest functional level. See: Exchange Server Supportability Matrix Martina Miskovic

Hi, For question on DC, it is recommended to post in AD forum http://social.technet.microsoft.com/Forums/en-US/winserverDS/threads Besides, Exchange 2003 is out of support. It is recommended to upgrade to higher version. Your understanding would be appreciated. Fiona Liao TechNet Community Support

What happens during a domain/forest functional level change? It is also important to know that during the process of raising DFL, the krbtgt password gets changed. However this change, together with other changes, should have no impact on an application that depends on Active Directory, but it should affect just the way that the domain controllers operate together as a group. Since raising functional levels is an irreversible operation (in many situations), it should be planned with some care and only after having verified that it will not affect any application that relies heavily on Directory Services, mostly the in-house written or third party ones. A lab environment in which testing them would be the best option, in case there are some concerns about them [for example some applications for which there had been problems during the 2008 R2 Operating System upgrade(s)], and its always strongly advisable to contact the vendor for having a confirmation that the product has been tested with the new functional levels. To resolve any krbtgt password reset issues and/or if you see Event ID 10 or 14 in your event viewer as an error, just reset the krbtgt account password twice. Steps listed here: Event ID 14 or Event ID 10. Exchange supportability matrix: Listed here is the supportability matrix for Microsoft Exchange Server: Exchange Server Supportability Matrix http://technet.microsoft.com/en-us/library/ff728623.aspx, in order to verify if the version of Exchange that the customer is using is supported/tested with the new functional levels.