Email

About Offline Global Address Lists (GAL) in Outlook.
Why you might encounter two different Offline GALs and how they function.

Cached Mode and Offline Address Book (OAB):

    Cached mode is the default configuration for Outlook.
    In this mode, your Exchange mailbox synchronizes with a local file (an .ost file),
    and the offline address list from your Exchange server synchronizes with a collection of files (.oab files) on your client computer.
    The offline address book contains essential user properties (such as email addresses and names) that Outlook requires.
    It allows Outlook to avoid connecting to the global catalog for name resolution or opening detailed records.
    When you're in cached mode, Outlook directly accesses the .ost and .oab files on your hard disk, minimizing network communication with the Exchange server.

Differences between Offline Address Book and Global Address List:

    The offline address book is a snapshot of the Active Directory directory service information available in the global address list.

    However, there are differences:
        Custom properties: The offline address book does not include custom properties added by administrators (e.g., Employee ID).
        Organization hierarchy: The offline address book lacks organization hierarchy information.
        Group membership: It also omits group membership details.

    When you're online (connection status: "Connected"), Outlook combines both the offline address book and the global address list to provide a complete listing of user information.
    But if you're offline (status: "Disconnected" or "Offline"), you'll see only the information available in the offline address book.

Old On-Prem Forest and New Forest:

    The incorrect data you're encountering likely stems from the old on-premises forest that you're phasing out.

    While you're now operating in the new forest, remnants of the old Active Directory data may still populate the offline address book.

    Ensure that your Outlook client is correctly configured to use the correct address book (the one from the new forest) to avoid discrepancies.

Verifying Address Book Selection:

    To verify which address book Outlook is using:

        Open Outlook.

        Go to File > Account Settings > Account Settings.

        Under the Data Files tab, select your Exchange account and click Settings.

        In the Advanced tab, check the Offline Address Book setting.

    Ensure that it points to the correct address book (from the new forest).

Remember that the offline address book is a crucial component for efficient Outlook operation, especially in cached mode.
If you encounter further issues, consider reaching out to your IT support team for specific troubleshooting related to your organization's setup.

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