Exchange 2007 Rollups and how they behave

Had an Exchange Rollup questions on Twitter over the past week, so asked around for some clarification. The question was "...downloaded rollup 1 and 4 and they both say rollup 9 when I launch them, can't install old rollups over new ones?" Here are responses from Dave Shackelford, Exchange MVP, and Scott Roberts, Test Lead for the Exchange CXP team.

From Dave Shackelford:

FWIW--Every new rollup includes all updates to date:
http://msexchangeteam.com/archive/2006/12/01/431722.aspx
So if there is a worry that an update hasn't taken effect, best to just rerun latest rollup, unless there is a suspected issue with it. But some rollups fix issues introduced by earlier rollups, so generally best to just run the latest.

Scott Roberts offered the following explanation of how the current rollups are working in Exchange 2007.

If you have Rollup 9 installed with a build version of 8.1.2345.003 and you try to install Rollup 6 with a build version of 8.1.1321.000, the UI experience that the customer will see is a combination of the RTM UI + the Rollup 6 UI + the Rollup 9 UI combined. The Rollup 9 UI will always win and be displayed since it is the latest version. It sucks and we tried to work around this but it is a MSI limitation. If you install Rollup 6 in the manner described, Rollup 6 will be installed correctly but it mostly is sitting in the MSI Cache and the newer Rollup 9 files will be what is on the box. If you uninstall Rollup 9, The MSI Service will take the RTM MSI and the Rollup 6 MSP and perform the reinstall action since rollup 9 (not 6) will no longer be on the box.

Rollup 9 contains all fixes that are in Rollup 6/7/8

Hope that helps.