Ignore Zombie Users registry parameter has been set

[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 http://go.microsoft.com/fwlink/?linkid=34707.]  

Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool checks the registry of the Exchange Server computer for the presence of the Ignore Zombie users registry entry. This registry value is present at:


If the Exchange Server Analyzer finds the Ignore Zombie users registry entry present and configured with a value of 1 or greater, a non-default configuration message is displayed.

In a mixed-mode Exchange Server organization that contains Exchange Server 5.5 and Exchange 2000 Server or in an environment that was previously mixed, problems may occur if the following conditions exist:

  • You upgrade the access control list (ACL) of mailboxes and public folders from Exchange Server 5.5 to Exchange 2000 Server.

  • The ACL contains user accounts that are not represented in the Active Directory® directory service.

These unused access control entries (ACEs) are also known as zombie users. As of the March 2003, post-Service Pack 3 Roll-up for Exchange 2000 Server, the default behavior for processing zombie users has changed. You can control this behavior by using the Ignore Zombie users registry key.

The Ignore Zombie users registry value can be used on servers that have Exchange 2000 Server Service Pack 3 or later installed. You should use this registry entry carefully and only when you are sure that the zombie users are not a result of Active Directory Connector (ADC) replication issues, such as latency. This registry value causes Exchange Server to ignore the zombie users and remove them from the ACL of the mailboxes or public folders. If the user is valid but is not in Active Directory at the time that the ACL was upgraded, the user is removed, and you have to manually add the user to each ACL later.

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.

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

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem

  3. In the right pane, locate and delete the Ignore Zombie users value.

  4. Close the registry editor, and then restart the Microsoft Exchange Information Store service for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, read the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=256986).

For more information about using the Ignore Zombie Users registry key, see the following Knowledge Base articles:


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