The Exchange 2007/2010 Offline Address Book (OAB) can be a pain to manage in environments where users expect instant access to updates to the Global Address List. Outlook 2007/2010 clients running in Cached Mode use the Offline Address Book by default for all address lookups. This means when a new user is added to your domain and mailbox enabled they will not appear in the "GAL" for Outlook clients until the OAB generation and distribution process has run it’s course. The following article explains how the OABGen and Web-Distribution process works in Exchange 2007 and 2010.


Process for OAB Generation and Web-Based Distribution:

  1. OABGen: This service runs on the OAB Generation server to create the OAB. This must be an Exchange 2007/2010 Mailbox server to support OAB Distribution.
    1. At 5:00am, the Exchange System Attendant service on OAB server generates new OAB files.
    2. The files are compressed and placed on a local share. (By default ExchangeOAB = <Exchange Install Folder>\ExchangeOAB)
  2. Exchange File Distribution Service: This service runs on the CAS servers and is responsible for getting the OAB content from the OABGen server.
    1. The CAS servers will attempt to download a new address book from the OABGen server on a polling interval (default 8 hours from the time the Exchange File Distribution Service was restarted).
    2. Not all CAS servers will download the new OAB at the exact same time.
  3. OAB Virtual Directory: The Exchange File Distribution Service will download the OAB from the OABGen server and place it in a directory on the CAS server. This location is an IIS virtual directory on a CAS server from which the OAB can be downloaded.
  4. Autodiscover: Clients use the Autodiscover process to locate the OAB download distribution point URL.
  5. Outlook Client downloads: This is the trickiest part of forcing an OAB update. The Outlook clients checks every 24 hours to see if there are any files in the OAB virtual directory with a timestamp 24 hours older than the OAB files stored locally. As far as I am aware, the only way to force an Outlook client to download a new OAB is to delete the OAB files stored locally on the client.
    The default location for OAB files on Windows Vista, 7, and 8: C:\Users\<current_user>\AppData\Local\Microsoft\Outlook


Troubleshooting your OAB issues:

Based on the process above there are a number of locations where the web-distribution of the OAB can break. In attempting to think this process through I created a process map. This map covers the basics of the troubleshooting, but at the second level I don’t go further because there could be any number of reasons for those services to break.




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