This update rollup is highly recommended for all Exchange Server 2010 SP3 customers.
For a list of changes that are included in this update rollup, see KB2891587.
This update rollup does not apply to Exchange Server 2010 Release To Manufacturing (RTM), Exchange Server 2010 Service Pack 1 (SP1) or Exchange Server 2010 Service Pack 2 (SP2).
For a list of update rollups applicable to Exchange Server 2010 RTM , Exchange Server 2010 Service Pack 1 (SP1) or Exchange Server 2010 Service Pack 2 (SP2), refer to the Knowledge Base article KB937052.
Download here: http://www.microsoft.com/en-us/download/details.aspx?id=41173
Until later,
Henrik Walther