The Track Duplicates registry entry is missing

[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: 2009-02-09

The Microsoft Exchange Server Best Practices Analyzer reads the following registry subkey to determine whether the Track Duplicates registry entry is present:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\<ServerName>\Private-<MailboxStoreGUID>\Track Duplicates

If the Best Practices Analyzer finds that the Track Duplicates entry is missing, the tool generates an error message.

If the Track Duplicates registry entry is missing, you may experience one or more of the following symptoms in the Exchange organization:

  • Exchange System Manager does not display mailbox sizes correctly. In this scenario, the mailbox size that appears in Exchange System Manager differs from the mailbox size that appears in Microsoft Office Outlook. Also, when you remove mailbox items, the mailbox size may not decrease as expected. In this scenario, Exchange 2003 does not reclaim the space that the deleted mailbox items used.

  • When you try to move mailboxes, the operation is unsuccessful, and the following event is logged in the Application log:

    Event Type: Error

    Event Source: MSExchangeIS Mailbox Store

    Event Category: General

    Event ID: 1205

    User: N/A

    Computer: <ServerName>

    Description: Failed to create the mailbox of /o=<organizationName>/ou=<organizationalUnit>/cn=Recipients/cn=<username> with error 0x4e3.

  • Exchange 2003 may not generate unread receipt messages for items that are deleted before they are read.

To address this issue, re-create the Track Duplicates registry entry.


This topic 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.

To create the Track Duplicates registry entry

  1. Click Start, click Run, type regedit, and then press ENTER.

  2. Locate and then click the following registry subkey:


  3. Create the following registry entry:

    Value name: Track Duplicates

    Value type: REG_ DWORD

    Value data: 1

  4. Exit Registry Editor.

  5. Dismount and then remount the affected information store databases. Alternatively, you can restart the Microsoft Exchange Information Store service.