The Exchange team is announcing today the availability of Update Rollup 6 for Exchange Server 2010 Service Pack 3. Update Rollup 6 is the latest rollup of customer fixes available for Exchange Server 2010 Service Pack 3. The release contains fixes for customer reported issues and previously released security bulletins. Update Rollup 6 is not considered a security release as it contains no new previously unreleased security bulletins. A complete list of issues resolved in Exchange Server 2010 Service Pack 3 Update Rollup 6 may be found in KB2936871. Customers running any Service Pack 3 Update Rollup for Exchange Server 2010 can move to Update Rollup 6 directly.
Read more at source: http://blogs.technet.com/b/exchange/archive/2014/05/27/released-update-rollup-6-for-exchange-2010-service-pack-3.aspx