Preferred Public Folder backfill source has been enabled

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at]  

Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads the following registry entry to determine whether Exchange has been configured with a preferred backfill source for the public folder hierarchy:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\<Server name>\Public-<Public Information Store GUID>\Preferred Backfill Source

If the Exchange Server Analyzer finds the Preferred Backfill Source registry entry present and configured, a non-default configuration message is displayed.

Exchange Server 2003 introduces a new Active Directory® directory service attribute named msexchPreferredBackfillSource that can be used to designate which Exchange Server should receive backfill request messages.

When a public folder has to replicate content, it sends out a query to the Exchange organization for a backfill request. The first public folder server to respond is used to backfill the data. This logic assumes that the first public folder server to respond is the closest; however, this may not always be the case. A configuration opportunity was introduced in Exchange Server 2003 that lets an administrator specify a preferred server for backfill.

In Exchange Server 2003, you can set the preferred server to use for backfilling public folder hierarchy and content using either an Active Directory attribute or the Preferred Backfill Source registry entry on the public folder server. The Active Directory parameter is checked first. If it is null, the registry parameter is checked. If that is also nonexistent, the default algorithm for public folder backfill is used.

To use the Active Directory attribute, set the Distinguished Name (DN) of the required backfill public folder store in the msExchPreferredBackfillSource attribute on the public folder store objects.

This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

If you choose to edit the msExchPreferredBackfillSource attribute in Active Directory, you will need to use an Active Directory editor such as Active Directory Service Interfaces (ADSI) Edit or the LDP (ldp.exe) tool.

If you incorrectly modify the attributes of Active Directory objects when you use ADSI Edit, the LDP tool, or another Lightweight Directory Access Protocol (LDAP) version 3 client, you may cause serious problems. These problems may require that you reinstall Microsoft Windows Server™ 2003, Exchange Server 2003, or both. Modify Active Directory object attributes at your own risk.

  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\<Server name>\Public-<Public Information Store GUID>

  3. Examine, and if desired, change the Preferred Backfill Source value. The value that should be entered is the Distinguished Name (DN) of the Exchange public folder store that you prefer to source from.

  4. If a change is made, dismount and remount the public information store for the change to take effect.

  1. Modify the affected Public Folder Store object's value for msExchPreferredBackfillSource to point to the desired backfill source. The msExchPreferredBackfillSource attribute can be found at:
    CN=Configuration, CN=Services, CN=Microsoft Exchange, CN=OrganizationName, CN=Administrative Groups, CN=AdministrativeGroupName, CN=Servers, CN=ServerName, CN=InformationStore, CN=StorageGroupName, CN=Public Folder Store

  2. The value that should be entered is the Distinguished Name (DN) of the Exchange public folder store that you prefer to source from.

  3. If a change is made, dismount and remount the public information store for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, see the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (

For more information about modifying Active Directory with the LDP tool, see the Knowledge Base article 260745, "XADM: Using the LDP Utility to Modify Active Directory Object Attributes" (