Earlier today Microsoft has been released roll up 6 for Exchange Server 2007 SP3.

For Exchange Server 2007 RU6 Download click here

For description of roll up 6 click here

Important issues which are resolved here are:

• 2575360 (http://support.microsoft.com/kb/2575360/ ) A new feature is available to automatically stop the Microsoft Exchange Information Store service when a time-out is detected in an Exchange Server 2007 SP3 environment
• 2545080  Users in a source forest cannot view the free/busy information of mailboxes in a target forest when the cross-forest Availability service is configured between two Exchange Server 2007 forests
• 2498852 (http://support.microsoft.com/kb/2498852/ ) “0x80041606” error message when you perform a prefix search by using Outlook in online mode in an Exchange Server 2007 environment
• 2572010 (http://support.microsoft.com/kb/2572010/ ) The Microsoft Exchange Information Store service may crash after you run the Test-ExchangeSearch cmdlet in an Exchange Server 2007 environment
• 2626217 (http://support.microsoft.com/kb/2626217/ ) Certain changes to address lists may not be updated in an Exchange Server 2007 environment
• 2656040 (http://support.microsoft.com/kb/2656040/ ) An Exchange Server 2007 Client Access server may respond slowly or stop responding when users try to synchronize the Exchange ActiveSync devices with their mailboxes

Note: Those who are running forefront security for exchange make sure that disabling the forefront before updating the roll up and enabling once it is done.

And also you could see this article here.