Earlier today the Exchange CXP team released Update Rollup 4 for Exchange Server 2007 SP3 to the Download Center.

This update contains a number of customer-reported and internally found issues since the release of RU3. For a list of changes included in this rollup, see KBA 2509911 Description of Update Rollup 4 for Exchange Server 2007 Service Pack 3. We'd like to specifically call out the following fixes which are included in this release:

• 2531208 You cannot synchronize a folder hierarchy by using Outlook for Mac 2011 in an Exchange Server 2007 SP3 environment
• 2528437 EWS applications cannot connect to Exchange Server 2007 servers after you make changes on accepted domains
• 2521063 You are incorrectly displayed as a meeting organizer after you synchronize the meeting by using your mobile device in an Exchange Server 2007 environment

Update Rollup 5 for Exchange Server 2007 Service Pack 3 is currently scheduled to release in August 2011.

Source: MSExchange Team