Offline Address book (OAB) Generation in Exchange and Outlook 2010

Offline Address book (OAB) Generation in Exchange and Outlook 2010

Offline Address book allows users to download the address book offline into the local machine. This local copy of the OAB File is used by outlook lookups when you are not connected to the network (working offline). It’s a complete copy of the global Address book.

I will try and explain how the OAB is generated, synchronized and made available for distribution to outlook users.

One Mailbox Server in the Organization is identified as OAB Generation Server. This is usually first mailbox server deployed in the organization or any mailbox server assigned with the OAB generation role during the later stage.

OABGen service running on the mailbox server helps to generate, creates and update all OAB files. OABGen service is part of the System Attendant Service. Any OAB files that are generated by default will be located in path “\Program Files\Microsoft\Exchange Server\V14\ExchangeOAB”.

OABGen communicates with the active directory and generates the address book for all the mailbox enabled users accounts, contact and other exchange resources in the Exchange organization. The files are compressed file with the extension .LZX format.

Now let’s I’m going to attempt and explain how OAB is distributed to the clients ?

There are two ways for Distribution in Exchange 2010. They are through web based distributions and through public folder distribution. Web based distribution is only supported with outlook 2007 clients and higher. OAB distribution through public folder is done by Exchange 2003 and is supported by all versions of outlook.

To keep this short and meaningful, I’m only going to talk about the web based distribution as public folder distribution is old news and not used anymore. Plus we are upgrading all outlook clients to Outlook 2010.

OAB files are generated in Exchange 2010 Mailbox server and outlook do not connect directory to the mailbox servers anymore. The solution approach is to use Client Access Server role with web based distribution. On the Client Access Server, a virtual directory called OAB runs with in the default web site. This virtual Director helps in distributing the OAB file.

How does the OAB virtual directory gets the OAB data files from the mailbox server ?

This is done by Microsoft Exchange File Distribution Service running on the Client access Servers. Microsoft Exchange File Distribution Servers polls the OABGen Server and copies the OAB data from the mailbox servers to CAS server. Once the complete OAB files are copied, if any data is then updated only that data is synchronized with CAS server. The synchronization or pol frequency is 8 hrs by default and you can change it if required using the following PowerShell cmdlets.

Set-OABVirtualDirectory "OAB (Default Web Site)" -PollInterval 360

If you get curious and wanted to know how the Web based distribution looks like. hold CTRL key and right click on outlook Icon system tray and Select “Email auto configuration” option from the menu.

Enter the User email address and password and click on Test. On the result tab you should be able to see what the OAB URL your outlook is connected to download the OAB from Exchange.

This is the quick info on how the OAB work in Exchange 2010. I hope this article helps you.