When you look at the properties of an Exchange server you see the version number specifed as... 8.1.0240.006, etc.. To match the numeric build of Exchange to the actual version refer to the link below for the matching matrix.
Microsoft Exchange Server 2007 8.0.685.24 or 8.0.685.25
December 2006
Microsoft Exchange Server 2007 SP1 8.1.0240.006
November 2007
Microsoft Exchange Server 2007 SP2 8.2.0176.002
August 2009
Microsoft Exchange Server 2007 SP3 8.3.0083.006
June 2010
Microsoft Exchange Server 2010 14.00.0639.021
October 2009
Microsoft Exchange Server 2010 SP1 14.01.0218.015
August 2010
Build numbers and release dates for Exchange Server
Article ID: 158530
http://support.microsoft.com/kb/158530
