"We strongly advise all customers install this newly released version of Microsoft Exchange Server 2010 SP1 Update Rollup 3 and to discard any prior version of RU3 (KB2492690) which you may have," stated Micrsooft.
RU3 Installation Guidance:
- Customers with RU3 already installed within your Exchange environment
It isn't necessary for you to uninstall the existing RU3 within your environment. The new RU3 package can be installed over the top of the existing package installed on your servers.
- Customers with previous SP1 RUs installed within your Exchange environment
You can simply install the new version of the RU3 package.
General RU Installation Guidance
- Note for deployments that leverage Forefront Security for Exchange: For those running FSE perform these important steps from the command line in the Forefront directory before and after this rollup's installation. Without these steps, Exchange services for Information Store and Transport will not start back up. You'll need to disable Forefront via "fscutility /disable" before installing the patch and then re-enable after the patch by running "fscutility /enable" to start it up again post installation.
Download: E2010 SP1 Update RU3
[Source: Exchnage Team blog]