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:

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.

To revert to the default configuration

  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" (

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