So this came out on the 16th Jan 2007, but I have just noticed the important bit in bold in it.
If you are using Microsoft Exchange Server 2003 Service Pack 2 (SP2) and you install this update, third-party services such as BlackBerry or GoodLink may be affected. Shared mailboxes and Microsoft Entourage delegation scenarios may also be affected.
Click the following article number to view the article in the Microsoft Knowledge Base before you install this update.
912918 Users cannot send e-mail messages from a mobile device or from a shared mailbox in Exchange 2000 Server and in Exchange Server 2003