Remember, if you are looking at the Global Address List in Outlook then you are NOT looking at the Servers Global Address List*.
If you are using Outlook 2003 or 2007 you may be in “Cached Mode”, and you are looking at a copy called the “Offline address book” This only gets updated Every 24 hours, and the copy on the server only gets updated every 24 hours at (by default).
In Exchange 2010 it takes even longer to synchronize the changes in the OAB than Exchange 2007.
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The offline address book contains the properties of a user, such as email addresses, that Microsoft Outlook requires to send an email message and display information about the sender.
Basically, this error is happening because Outlook 2007 and higher clients rely on web based distribution of the offline address book, and that address book is not found on the CAS Server.
The fix is to enable the Default Offline Address book on the mailbox server for Web-based distribution: This setting does not go into effect immediately.
The offline address book is a snapshot of information from the Global Address List (GAL).
Therefore, not all the information in the GAL is available in the offline address book.
If you are in Cached Exchange Mode and your connection status is Disconnected, Trying to Connect, or Offline, you can see only the information that is in the offline address book.
Note: If you are using Cached Exchange Mode, we recommend that you download the full details of the offline address book.
Support for Outlook 2000 was dropped with Exchange 2007, Exchange 2010 only supports Outlook 2003 (post SP2). In the diagram below you can see this server is performing public folder AND web based distribution, this is probably because you ticked this box when you installed the product.
Exchange 2013 only supports Outlook 2007 (post SP3 and cumulative update), and Outlook 2010 must be at SP1 with cumulative update. For public folder distribution ensure the public folder database is mounted, and at least one server holds a replica.
The offline address book size can vary from several megabytes to hundreds of megabytes in uncompressed form.