This update is required if the Offline Address Book (OAB) generation is moved from an Exchange 2007 server to an Exchange Server 2003 Service Pack 2 (SP2) server. It resolves issues which are caused due to changes in the OAB version 4 in Exchange 2007. This update is also recommended if the OAB is generated on an Exchange Server 2003 SP2 server after Exchange 2007 is deployed in the Exchange organization.

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Microsoft, Exchange 2003, KB 922817