This post is a list of Microsoft Exchange versions, build numbers, Update Rollups and Cumulative Updates that I keep up to date.
The latest version is Exchange 2019 Cumulative Update 6 which was released on 16 June 2020.
Microsoft Technet has some really useful articles at the links below detailing all the Exchange Service Pack and Update Rollup build numbers since Exchange 2003.
Since this page was first created Microsoft has now combined the two source pages itself into one Exchange Server Updates: build numbers and release dates page which can be found at the link below.
The tables below are a snapshot of the link as of June 2020.