Outlook offline address book not updating
If Outlook is left running constantly in Cached Exchange Mode, it automatically updates the offline address book about one time per day depending on updates on the computer that is running Exchange.
The offline address book size can vary from several megabytes to hundreds of megabytes in uncompressed form.
This reduces network traffic and improves performance.
The offline address book is a snapshot of information from the Global Address List (GAL).
Quite often all Administrators, even Exchange Administrators simply refer to the users they see in the Address section of Outlook casually as the GAL for ease of reference, but really more often than not, you are looking at the OAB.
GAL Objects are directly viewable in the Exchange Management Console/Shell and OWA and Microsoft Outlook BUT ONLY IN ONLINE MODE – The GAL will only present objects that have AD Attributes beginning with ms EXCH* (and some others) populated that it uses to filter on.
If these attributes are present, then the AD Objects that are Mail-Enabled or Mailbox-Enabled will appear in the GAL – and ultimately the Offline Address Book.
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.
By using an offline address book, Outlook doesn’t have to connect to Microsoft Exchange Server to resolve names or open the records for each user.