My research suggests this is possible but I wanted to throw it out there for those that can confirm this in real world use scenarios.
I have Windows 2003 R2 SP2 DC's, 1 Windows 2008 R2 SP1 DC and 2 Windows 2012 R2 DC's.
The Domain Functional Level is Windows Server 2003.
I am currently running Exchange 2007 SP3 RU13 on separate non-DC servers.
Before I upgrade Exchange from 2007 to Exchange 2013 I would like to move the FSMO roles from the Windows 2003 DC's over the Windows 2012 R2 DC's then decommission the Windows 2003 DC's keeping the Domain Functional Level at Windows Server 2003.
Does anyone see any issues with this so far? Should I move the FSMO roles over to the Windows 2008 DC instead?
Also if someone can confirm that these steps are best practice....
1. After the above is complete I will install Exchange 2013 onto a Windows 2012 R2 Server
2. Move everything over from Exchange 2007 to Exchange 2013
3. Decommission the last of the Windows 2003 servers that Exchange 2007 was running on.
4. Bump the Domain Functional Level up to Windows 2008 R2 SP1
5. Decommission the Windows 2008 R2 SP1 DC
5. Bump up the Domain Functional Level to Windows 2012 R2
Thank you in advance for your comments!