Users Missing From Global Address List
In Microsoft Outlook 2003/2007 and above, when using Microsoft Exchange Server 2003/2007, some users do not appear in the Global Address List (GAL).
This may occur if the user's default email address in Active Directory Users and Computers is different to the default reply address as appearing in the Exchange Management Console (Recipient Configuration → Mailbox) under E-Mail Addresses.
Once corrected, the change should be reflected in the Offline Address Book when it is next updated, and then downloaded to clients automatically. But if you prefer it to happen immediately, update the OAB in Exchange Management Console, wait about 10 minutes, then manually update Outlook's copy on workstations.