How Is Offline Address Book Distributed In Exchange 2010…

A clear understanding of how the offline address book works in exchange helps an admin in troubleshooting the related issues. This article explains how OAB gets generated and distributed in Exchange 2010.

The Exchange System Attendant service is responsible for the generation of oab. This service is available only on a server that has the mailbox role installed. To find out the server that is generating the offline address book in your organization, launch EMC –> Organizational Configuration –> Mailbox –> OAB tab.

OAB Generation Server

If you have made changes in Exchange, you can update the address book by right clicking the Offline Address Book and selecting Update. By default, oab is updated only once in 24 hours at 5am. You can customize the update schedule depending upon your requirements.

Update OAB

You can use the Shell as well to update OAB. Run Update-OfflineAddressBook –Identity “Default Offline Address Book”

Where exactly are these oab files stored? On a default installation, the oab files are stored in C:Program FilesMicrosoftExchange ServerV14ExchangeOAB. This folder is shared so that it can be replicated to the CAS server for web distribution. Within the ExchangeOAB folder, there will be a folder with GUID name which holds the actual OAB files for distribution.

OAB files in mailbox server

The files with “lng” in its name (towards the end) are for Windows machines whereas the one that has “mac” in its name are for Mac clients.

How does oab end up in public folders? Outlook 2003 and previous versions get oab from the system public folders in exchange. The oab generation server opens the oab folders and updates the file.

How does Outlook 2007 & 2010 get oab files? Outlook 2007+ clients use autodiscover to find the OAB url and use that to connect to the corresponding server that hosts the oab files for distribution. The CAS server is responsible for providing oab files for outlook 2007+ clients. For that, CAS server runs a service named Microsoft Exchange File Distribution Service which copies the oab files from the mailbox server (ExchangeOAB folder) to the web distribution point in the CAS server.

Where is this web distribution point, one might ask? The web distribution point is a folder in the file system where the copied oab files are placed. The default location is C:Program FilesMicrosoftExchange ServerV14ClientAccessOAB.

OAB Web Distribution Point

The web distribution point is updated once in 8 hours. If you want to force an oab update, run Update-FileDistributionService –Identity “servername” –Type OAB. Alternatively, you can also restart the Exchange File Distribution Service.

Update FDS

Now that you know how oab works and are replicated from the mailbox server to the system folders & web distribution point, you will find it much easier to troubleshoot any issues relating to the offline address book.

  1. Is there a difference on how OAB works under the 2 scenarios.

    1. Internal users not using OA – but have Cached exchange mode on
    2. Internal users not using OA – and cached exchange mode is off

    And can you specifically call out what service is being called – the flowchart of services the client must speak with under both scenarios?

    If so that would be great. Your page is the closest I have found so far that describes how there is a URL passed back to the client with it on which i wasn’t aware of.

    Thank you very much in advance.



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