How to determine the version of Exchange and Exchange Service Pack level

http://support.microsoft.com/kb/152439

Also try running the following commandlet from an Exchange Management Shell:

Get-ExchangeServer -Identity ExServer1 | Format-Table Name, AdminDisplayVersion

Full list of the Exchange Server Updates with build numbers and release dates:

https://technet.microsoft.com/en-us/library/hh135098(v=exchg.150).aspx