Offline Address Books, fondly referred to as OABs, are a critical component in Exchange infrastructure for a long time now. An OAB is used by Microsoft Outlook clients in Cached Exchange Mode for address book lookups when offline. OABs are also critical in reducing the workload on Exchange servers as cached mode Outlook clients will always query the local OAB first.
The OAB has evolved over Exchange releases. The last major overhaul of OAB architecture was in Exchange Server 2007, where we introduced web-distribution of OAB along with CAS server role taking major responsibility of distributing the OAB. But the OAB generation process itself hasn't changed much.
With the change in the server role architecture introduced in Exchange Server 2013, we have also changed the way OABs are generated and distributed to clients. Let’s explore the new OAB in Exchange 2013 by comparing it to its predecessors.