Microsoft has released Update Rollup 6 for Exchange Server 2010
Update Rollup 6 for Exchange Server 2010 resolves issues that were found in Exchange Server 2010 since the software was released. This update rollup is highly recommended for all Exchange Server 2010 customers.Update Rollup 6 for Exchange Server 2010 (KB2608646)
For a list of changes that are included in this update rollup, see KB2608646.
This is a cumulative update rollup and replaces the following:
KB976573 Update Rollup 1 for Exchange Server 2010 (KB976573)
KB979611 Update Rollup 2 for Exchange Server 2010 (KB979611)
KB981401 Update Rollup 3 for Exchange Server 2010 (KB981401)
KB982639 Update Rollup 4 for Exchange Server 2010 (KB982639)