Understanding Domain and Forest Level’s in Windows Server environment
Microsoft has since active directory publication (2000) different domain and forest level’s published. They generally follow the windows server edition’s like 2000, 2003 and now 200´8 (R2). Each level has his own feature set and compatibility requirements on domain controller side. For some applications which are active directory integrated like Exchange it is really important to have the right configuration in your active directory environment.
How Active Directory Functional Levels Work
Active Directory Functional Levels Technical Reference
What Are Active Directory Functional Levels?
Exchange 2007 System Requirements
Exchange 2010 System Requirements
Regards
Ramazan