How Exchange 2007 OAB Files are replicated to a Client Access Server for download

In prior versions of Exchange the Offline Address List files would reside in the form of an OAB message and attachments that were posted to an OAB system folder.

In Exchange 2007 the Offline Address List files can reside in a few places:

  • In a public folder information store (if client legacy support is enabled) created

  • On the OAB Generation Server

  • On multiple distribution points (Other CAS servers).

This is really important to understand because if you are not aware of where these files reside or how they get to the other servers you will not know where to start troubleshooting.

Following FDS replication of an Offline Address List
The FDS (File Distribution Service) is a new component that is installed on the Client Access Server. This component is responsible for the replication of OAB files from the OAB Generation server to the Client Access Server. The FDS has a default polling interval and will contact the Active Directory once it's polling frequency has been hit (default 480 minutes), or if the following notifications have been sent to FDS to state otherwise:

  • A new Offline Address Book has been created

  • An Offline Address Book needs to be published

  • The polling interval has been changed or the polling interval is up

  • The file paths change

  • The OAB Generation server changes

There are a few key things that I need to point out before we go further. 

1.     By default the OAB share on the OAB Generation server (local distribution point) will not be present.  This directory gets created the first time the OAB Generation creates the Version 4 Offline Address List.  

  • Local directory [C:\Program Files\Microsoft\Exchange Server\ExchangeOAB]

  • Unc path [\\ExchangeServerName\OAB\<GUID of OAB>]

      2. Once the Distribution Point share has been created it will contain sub directories.
      3. Each sub directory will be named with the the GUID of the Offline Address Book.
      4. Each OAB directory will contain a set of files that will be downloaded by the client.

All files in the directory will be specified in the oab.xml file. This is the file that the Outlook client will use so it can determine which OAB files it download. If these files or directories are not present this can result in Outlook client synchronization errors, as there will be no files for the client to download.

The process from start to finish
1. The OAB Generation Servers generates a Version 4 Offline Address List.

2. At the end of the generation the files will reside in the System Attendant Mailbox as this is the master location. The files are then copied from the System Attendant Mailbox to the local distribution share on the OAB Generation Server.

3. At this point the files can be downloaded from the OAB Generation Server by an Outlook client.

4. A notification is sent to the FDS service on the Client Access Server that there are files to be replicated.
5. The FDS will then start replication of the files to the remote distribution points where they may be.

Below is a copy of the information event that you will see on the Client Access Server when an Offline Address List has been successfully replicated.

Event Type: Information
Event Source: MSExchangeFDS
Event Category: FileReplication
Event ID: 1008
Date:  8/25/2006
Time:  6:05:41 PM
User:  N/A
Computer: E12-CAS
Process MSExchangeFDS.exe (PID=620). Offline Address Book data synchronization task has completed successfully. OAB name: "Test", Guid: 1fd83cb9-8887-4bbd-83f2-59c8a5ab29a4

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