It is recommended that for each Windows user profile, not more than one Outlook profile use the offline address book. One Windows user profile can be configured to use multiple Outlook profiles, and that user profile can potentially download an offline address book for each Outlook profile. However, Outlook can only support applying changes to one offline address book for each Windows user across all Outlook profiles.

Note:
Multiple Cached Exchange Mode profiles that use offline address books for one Windows profile can cause unintended effects. If the Windows profile alternates between Outlook profiles, each Outlook profile must download the full offline address book.

After downloading the offline address book files the first time, Outlook does not have to download the entire offline address book again unless it has changed significantly. Typically, Outlook only has to download updates. If the updates amount to more than one-eighth the size of the offline address book (as stored on the server), Outlook downloads a full new set of files.

For a more extensive discussion of the changes that cause Outlook to download a full offline address book, see Microsoft Knowledge Base article 839826, "High network usage occurs while Outlook clients download the offline Address Book from Exchange 2003 at the same time." These details are especially relevant if Outlook communicates with the Exchange servers using a slow WAN link, or if you are making major changes to a large address list. For information about controlling the impact of such downloads on your system, see Microsoft Knowledge Base article 867623, "Throttling full offline Address Book downloads to limit the effect on a LAN in Exchange Server 2003."

By default, Outlook stores the offline address book files on the client computer in the following location:

\Documents and Settings\<Windows alias>\Local Settings\Application Data\Microsoft\Outlook\

This location can be changed by editing the registry. Before you edit the registry, close Outlook, and create the appropriate file path (for example, D:\OAB).

For detailed steps about how to change the default file path of the offline address book files, see How to Change the Default File Path of the Offline Address Book Files.

The following tables list the files that Outlook downloads to the client computer. You can use this information when troubleshooting offline address book issues.

Files downloaded by Outlook 2003 in ANSI (Non-Unicode) mode, Outlook 2002, and Outlook 2000

Files downloaded by Outlook 2003 in Unicode mode

By default, Outlook 2003 uses the Full Details Unicode offline address book. If you upgrade to Outlook 2003 using existing Outlook profiles, Outlook 2003 uses the ANSI offline address book. Outlook 2002 and Outlook 2000 use the ANSI offline address book.

Sometimes you can find both ANSI and Unicode files in the local directory of a client computer, but Outlook will only use one of these files. For example, in some cases when Outlook switches between ANSI and Unicode mode, or if Outlook is upgraded from an earlier version to Outlook 2003, both sets of files may exist. However, Outlook 2003 uses only one set of files.

To verify if Outlook 2003 is running in Unicode mode, see "Verifying the Outlook 2003 Configuration" later in this topic.

By default, Outlook 2003 Cached Exchange Mode is configured to use the offline address book. Outlook downloads the offline address book assigned to the user when it synchronizes the user's mailbox for the first time. For more information about multiple offline address books and how to select the offline address book, see "Configuring Outlook 2003 Classic Offline Mode" later in this topic.

After Outlook completes a full offline address book download, it checks for updates every 24 hours from the last successful update. You can modify the way Outlook uses the offline address book in the following ways:

• Set up a send/receive group to check for updates more frequently.
  
• Modify the type of automatic download.
  
• Configure Outlook to use the online address list for resolving ambiguous names.
  

For information about Outlook 2003 Cached Exchange Mode, see Outlook 2003 Help.

Outlook 2003 Cached Exchange Mode does not require send/receive groups for synchronizing the offline address book, and it does not include the offline address book in the default send/receive group. If Outlook is running in classic mode instead of cached mode, it does include the offline address book in the default send/receive group.

Under certain circumstances, the user may require a send/receive group. For example, if the user wants Outlook to check for changes every hour instead of every 24 hours, the user can configure an appropriate send/receive group.

Important:
Automatic offline address book downloads in Cached Exchange Mode cannot be controlled through the send/receive groups.

For detailed steps about how to manage send/receive groups, see How to Manage Send/Receive Groups in Outlook.

If the user chooses to use a send/receive group, Outlook checks for changes to the offline address book, and the user is not provided with an option to do a full download with the send/receive group. For more information about working with send/receive groups, see Outlook Help.

Outlook 2003 includes optimizations to prevent excessive full downloads and to ensure that the offline address book is downloaded at the appropriate time. There are four download settings: Download Full Items, Download Headers and then Full Items, Download Headers, and On Slow Connections Download Only Headers. (For information about how these download settings are selected, see the following figure.) By default, when one of the header options is selected, offline address book downloads are disabled.

If a user sets the On Slow Connections Download Only Headers option (generally for a dial-up connection), Outlook downloads only headers. This action makes sure that Outlook does not use the limited bandwidth of slow connections for address book updates.

The four automatic download types that are available in Cached Exchange Mode

To prevent overloading the network, Outlook will retry failed full offline address book downloads at 13-hour intervals. If a full offline address book download is interrupted, Outlook has to restart the download. Outlook retries failed change downloads every hour until it succeeds.

In Cached Exchange Mode, Outlook 2003 uses the offline address book when it resolves ambiguous names, even when connected to the server. Outlook tries to resolve ambiguous names when a user types an address in the To line of a message, and when the user sends the message.

Searches for ambiguous names in the offline address book will only find results using the Display Name, Last Name, the Nickname, and the Office Location.

For detailed steps about how to configure all cached mode clients to use the online global address list to resolve ambiguous names, see How to Configure All Cached Mode Clients to Use the Online Global Address List to Resolve Ambiguous Names.

When the user chooses to work offline for the first time, Outlook prompts the user to configure their offline folder files (.ost files) and the offline address book files. Outlook also adds the offline address book to the default send/receive group. If users desire, they can also download the offline address book manually.

For detailed steps about how to download the offline address book manually see How to Download the Offline Address Book Manually.

Use the following procedures to help troubleshoot offline address book issues with Outlook 2003.

For detailed steps about how to verify that Outlook 2003 is using the offline address book, see "How to Verify That Outlook 2003 Is Using the Offline Address Book".

For detailed steps about how to verify that Outlook 2003 is running in the Unicode mode, see "How to Verify That Outlook 2003 Is Running in the Unicode Mode".

For detailed steps about how to verify that Outlook 2003 is running in Cached Exchange Mode, see "How to Verify That Outlook 2003 Is Running in Cached Exchange Mode".

Unlike earlier versions of Outlook, Outlook 2003 no longer writes logs to the Deleted Items folder. Instead, if the offline address book is not successfully synchronized, a message is logged in the Synchronization Failures folder in Outlook.

Outlook 2002 and Outlook 2000 use the offline address book in a way that is similar to Outlook 2003. However, there is no Unicode support (no offline address book version 3a support), and no Cached Exchange Mode. Also, if the offline address book is not successfully synchronized, a message will be logged in the Deleted Items folder. This behavior differs from that of Outlook 2003.

Finally, there is a known issue with Outlook 2000 where the e-mail message is sent to the incorrect recipient. To avoid this issue, see the following Microsoft Knowledge Base articles:

• 820838, "OL2000: E-mail Messages That You Created While Offline Are Sent to the Wrong Recipient"
  
• 232767, "OL2000: Integrity Check For Client OAB"