Microsoft has released Update Rollup 4 for Exchange Server 2010

Update Rollup 4 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.

For a list of changes that are included in this update rollup, see KB982639.

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)

  Update Rollup 4 for Exchange Server 2010 (KB982639)