Found this and thought I should share it
Source: http://support.microsoft.com/default.aspx?scid=158530
Each version of Exchange Server and Exchange 2000 has a different build number. Listed below are the build numbers and general release dates for each version:
Name Version Release Date
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Exchange 4.0 4.0.837 April 1996
Exchange 4.0 (a) 4.0.993 August 1996
Exchange 4.0 SP1 4.0.838 May 1996
Exchange 4.0 SP2 4.0.993 August 1996
Exchange 4.0 SP3 4.0.994 November 1996
Exchange 4.0 SP4 4.0.995 April 1997
Exchange 4.0 SP5 4.0.996 May 1998
Exchange 5.0 5.0.1457 March 1997
Exchange 5.0 SP1 5.0.1458 June 1997
Exchange 5.0 SP2 5.0.1460 February 1998
Exchange 5.5 5.5.1960 November 1997
Exchange 5.5 SP1 5.5.2232 July 1998
Exchange 5.5 SP2 5.5.2448 December 1998
Exchange 5.5 SP3 5.5.2650 September 1999
Exchange 5.5 SP4 5.5.2653 November 2000
Exchange 2000 6.0.4417 October 2000
Exchange 2000 (a) 6.0.4417 January 2001
Exchange 2000 SP1 6.0.4712 July 2001
Exchange 2000 SP2 6.0.5762 December 2001
Exchange 2000 SP3 6.0.6249 August 2002
Exchange 2000 post-SP3 6.0.6487 September 2003
Exchange 2000 post-SP3 6.0.6556 April 2004
Exchange 2000 post-SP3 6.0.6603 August 2004
Exchange Server 2003 6.5.6944 October 2003
Exchange Server 2003 SP1 6.5.7226 May 2004
To view the build number of your server, see the properties of the server