Microsoft released Update Rollup 1 for Exchange Server 2007 SP3 that includes new fixes for: Client Access; Edge Transport; Hub Transport; Mailbox; Unified Messaging. For full list of fixes, see KB 2279665. This update rollup doesn't apply to Server 2007 RTM, or SP1 or SP2, refer KB937052.
A fix for Exchange 2007 SP3 and OWA S/MIME Version Mismatch is included in this release:
KB 980301 Exchange Information Store service stops responding during a Volume Shadow Copy Service backup on an Server 2007
KB 983529 EdgeTransport.exe process crashes and then restarts on an Server 2007
KB 973637 Server 2007 creates incorrect Lotus Notes proxy email addresses
KB 982928 Msftesql.exe process continues using memory on Server 2007
KB 983296 Exchange ActiveSync crashes on an Server 2007 causing client synchronization to be unavailable
More Info: Download