Microsoft has released Update Rollup 2 for Microsoft Exchange Server 2007 Service Pack 3 (SP3).
We can refer to the article Description of Update Rollup 2 for Exchange Server 2007 Service Pack 3 to know issues that the update rollup fixes And download it from Download the Exchange2007-KB2407025-EN package now.
Before you install an update rollup or a service pack, visit the following Microsoft website for prerequisites, installation instructions and known issues:
How to Install the Latest Service Pack or Update Rollup for Exchange Server 2007 (http://technet.microsoft.com/en-us/library/ee221147(EXCHG.80).aspx)
For a list of update rollups that apply to Exchange Server 2007 RTM, Exchange Server 2007 SP1 or to Exchange Server 2007 SP2, the following Microsoft website: