Update Rollup 6 For Exchange 2010 SP3 has been released (KB2936871)
We have also released Update Rollup 6,RU 6, for Exchange Server 2010 Service Pack 3.
You can read about all the details on :
To get the RU6 just follow this link :
The complete list of issues resolved in Exchange Server 2010 Service Pack 3 Update Rollup 6 can be found in KB2936871