Offline Address Book Technical Overview
Topic Last Modified: 2005-10-11
This topic provides a brief technical overview of offline address books. It discusses how offline address books are generated, and where offline address book objects are stored in the Active Directory® directory service.
Microsoft® Office Outlook® 2003 uses the offline address book to provide offline access to directory information from the global address list (GAL) and from other address lists. Each night, Exchange generates new offline address book files and places them in a special public folder, known as a system folder, for Outlook to download. The offline address book files are compressed before they are added to the offline address book system folders so that the download to Outlook is minimal. Outlook is scheduled to check periodically for new offline address book files in these system folders, and download the required files.
Outlook 2003 has many new features and enhancements that are related to the offline address book. By using the offline address book, Outlook does not need to connect to Active Directory for common operations such as resolving recipient names, browsing the address list, or retrieving address details. The available functions are limited, but they are similar to the GAL (and other address lists) when working on the network.
Several Exchange Server components work with Active Directory to generate and maintain offline address books. After an offline address book has been created (either automatically by Exchange Setup or manually by an administrator using Exchange System Manager), Exchange Server and Active Directory work together to maintain the offline address book, keeping it synchronized with changes that may be made in the directory.
System folders can be displayed in Exchange System Manager, enabling an administrator to view the files that make up the offline address book. The following figures shows the Offline Address Book system folders in Exchange System Manager.
For detailed steps, see How to View the Offline Address Book System Folders in Exchange System Manager.
Each of the Exchange Server and Active Directory components involved in generating and maintaining offline address books is described as follows:
Microsoft Exchange System Attendant Responsible for generating the offline address book. The System Attendant calls Oabgen.dll. This is a MAPI application (referred to as OABGen) that reads from Active Directory. On a server running Exchange Server 2003 SP2, the first time an offline address book is created, OABGen creates the OAB Version 2, OAB Version 3a, and OAB Version 4 folders. You can specify the versions of offline address books that are generated. For detailed steps, see How to Specify the Versions of Offline Address Book to Be Generated.
Note: On a server running Exchange Server 2003 SP1, the first time an offline address book is created, OABGen creates the OAB Version 2 and OAB Version 3a folders.
Every time OABGen runs, it performs several tasks:
It creates the files for all offline address book versions.
It compresses the files.
It creates posts in the system folders for each version of the offline address that it is configured to generate. The offline address book files will be saved as attachments on the posts in the folders.
It creates incremental offline address book files containing daily changes. The default setting in Exchange Server 2003 is to generate an offline address book incremental file every morning at 05:00.
Microsoft Exchange Information Store Responsible for storing the offline address book system folders listed directly under the OFFLINE ADDRESS BOOK. Each time a new offline address book is created, the corresponding offline address book system folders are created, including the containers, such as EX:/o=<Organization Name>/ou=<Administrative Group>, and /o=<OrganizationName>/cn=addrlists/cn=oabs/cn=<name of Offline Address List> during nightly online maintenance.
Directory servers Active Directory servers are utilized in the offline address book generation. Offline address book configuration data is stored in the Configuration Naming Context partition in Active Directory, making it available to all domain controllers. In addition, global address list information is stored in global catalog servers.
Recipient Update Service Although offline address book generation does not require the Recipient Update Service, address lists do require this component. The System Attendant calls the Recipient Update Service, which in turn maintains the address list membership on recipients. If the address list is blank, the offline address book generation will fail.
A properly configured Active Directory is a necessary component for offline address book generation to work correctly with Exchange Server 2003. In addition to address lists, and the objects that make up those lists, the offline address book has its own directory attributes. Issues with Active Directory could result in issues with the offline address book. For example, interruptions in or a failure of Active Directory replication could prevent newly added directory objects from appearing in the offline address book.
Offline address book information is stored in two places. The offline address book content is stored in the NON IPM SUBTREE of the public folder hierarchy, and offline address book objects are stored in the Configuration Naming Context in Active Directory (under CN=Offline Address Lists,CN=Address Lists Container,CN=<OrganizationName>,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=<DomainName>,DC=<DomainNameExtension>). Like all directory objects, offline address books have several attributes that control behavior and other elements.