Overview of Configuring Offline Address Books

          The offline address book is used by Outlook clients when you configure the clients to use a cached mode Outlook profile, or when the client is in offline mode. It is cached on the local client so that users can search the GAL when sending messages.
          The default offline address book contains the entire GAL, which includes all recipients in the Exchange organization. You can create additional GALs and add them to a custom offline address book.
          By default, the offline address book is generated on a Mailbox server only once each day at 5 a.m. This means that any additions, deletions, or changes made to mail-enabled recipients are only committed to the offline address book once daily, unless you modify the schedule to generate the offline address book more frequently.