In all previous Exchange releases, OAB generation was bound to a specific Exchange server. 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. The unbinding of OAB from a specific server allows the same OAB to be generated by multiple Mailbox servers. This new architecture provides greater resiliency in OAB generation.

Also, In Exchange 2013, the OAB files are generated and stored in the Organization Mailbox first and later copied to the %ExchangeInstallPath%\ClientAccess\OAB\. In Exchange 2013, OAB files are not stored locally on the CAS. CAS 2013 proxies all OAB download requests to the appropriate Exchange 2013 Mailbox server. So Microsoft Exchange File Distribution Service is removed from the CAS role.

I am trying to explain the conventional methods for forcing the OAB generation in Exchange 2013 and fresh download on an Outlook 2013 environment. This is some times required in case your OAB generation/download is not properly working.

There are two methods available in server side to generate new Offline Address Book

1. Update-OfflineAddresBook: Following cmdlet will force OAB generation of an OAB named “Default Offline Address Book” across all organization mailboxes. This command initiates an RPC request to each mailbox server hosting an active organization mailbox.

Update-OfflineAddressBook “default offline address book”

2. Restart the Mailbox Assistant service: The Microsoft Exchange Mailbox Assistant service on Mailbox Role is responsible for generating OAB. Restarting this service generates all OAB’s defined in the environment on a specific mailbox server, if it’s hosting an active organization mailbox.

Next, we will see how we can delete the existing oab files associated with an Exchange 2013 account accessed by Outlook 2013 in a Windows 8 machine and download the newly generated oab from the server

In outlook 2013 installed on Windows 8, the offline address book is placed on: C:\Users\Manu\AppData\Local\Microsoft\Outlook\Offline Address Books\<guid>. Note that if you are having multiple outlook profiles, you may see multiple GUIDs in the folder.

You may see the following file structure with in the GUID corresponding to the outlook profile in consideration.

I am going to rename the corresponding GUID folder as shown below (Exit Outlook first), to initiate a fresh oab download.

Now, I am initiating an oab download as follows:

Now, Check the OAB files location and see a new folder has created with the same GUID name and the oab file contents