The update rollup 1 for Exchange Server 2010 Service Pack 2 is now available for download. Please download your copy of Update RU1 for Exchange Server 2010 SP2 from Microsoft Download Center.
As always, ensure that you disable Forefront Protection for Exchange users before you proceed with the installation and enable it once you finish the activity. This is to ensure there are no impact on your Tranport and Information Store services.
For more details about the issues addressed by this update, please see KB 2645995
The installation goes smooth, however it takes a long time for preparing for installation(took almost 20+ min). Until the completion of it preparation stage, the installation process will not affect the exchange functionality.
MS has blogged about an issue reported about this RollUp.There is a temporary incompatibility between SP2 RU1 servers and servers running earlier versions of Exchange where an Exchange 2010 SP2 RU1 Client Access server is proxying request to earlier version of Exchange CAS servers.
To know more, see Exchange 2010 SP2 RU1 and CAS-to-CAS Proxy Incompatibility