Microsoft has published a document that describes the Exchange schema extensions to the Active Directory. The Word document (packaged in an MSI file) can be downloaded here will be. The document also shows that Exchange Server 2010 Service Pack 2 makes changes to the schema.
The document contains the schema changes for Exchange Server 2003, 2007 and 2010.
http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=5401
