It seems currently there are so many different versions of Windows/Active Directory we can all easily get confused to what Exchange Server version is supported on which OS/Active Directory.
Luckily there is a support matrix that explains this very clearly!

Below is a screenshot of the Active Directory Support Matrix (Double click below to see the full matrix)

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On this page there is information for Support Matrix:

  • Release Model
  • Supported Operating System Platforms
  • Supported Active Directory Environments
  • Web Browsers That Are Supported for Use with the Premium Version of Outlook Web Access
  • Web Browsers That Are Supported for Use with the Basic Version of Outlook Web Access µ
  • Web Browsers That Are Supported for the Use of S/MIME with Outlook Web Access
  • Clients
  • The Microsoft .NET Framework
  • Windows PowerShell
  • Microsoft Management Console
  • Windows Installer

Exchange Server Supportability Matrix:
http://technet.microsoft.com/en-us/library/ee338574.aspx