There are following criteria which should be fulfilled before deployment and configuration of DPM for Exchange database protection.
I’m giving it a 99% chance that you will (and if you don’t you have a serious problem at hand!
The disadvantage with this approach was that only one server was configured for OAB generation, and it was a single point of failure.
In Exchange 2013, the OAB is generated by each Exchange 2013 Mailbox server(s) that hosts a special type of arbitration mailbox, called organization mailbox.
For Users where Outlook is in Cache mode, They got to have their Outlook Address book Updated ,when they can access the latest Address book while they go offline.
If Outlook is left running constantly in Cached Exchange Mode, it updates the Offline Address Book automatically about once a day, depending on Address Book updates on the server running Exchange.