Non-default SMTP MaxLdapConnections registry value

[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 the default MaxLdapConnections has been changed:


If the Exchange Server Analyzer finds that the MaxLdapConnections registry value has been manually created, changing the default Exchange server binary setting of 8, the Exchange Server Analyzer displays a non-default warning message. By default, the MaxLdapConnections registry value is not created by an Exchange installation. However, MaxLdapConnections registry value can be manually created after the Exchange installation to change the value. The MaxLdapConnections value sets the maximum number of LDAP connections that the categorizer opens to a single global catalog server. If the registry value is manually created and the setting for the registry value is configured incorrectly, the Exchange server may experience message transport problems.


The MaxLdapConnections registry value should match the value for the HKEY_LOCAL_MACHINE System\CurrentControlSet\Services\SMTPSvc\Parameters\MaxPoolThreads registry value setting at all times.

It is recommended that the MaxLdapConnections registry value be created or modified only after careful consideration. The default values in the binaries for Exchange server were carefully selected for optimal performance for use in most Exchange server environments. A general best practice is to address the root cause of the problem instead of modifying the default behavior of Exchange Server by manually configuring the registry. To comply with best practices, if the MaxLdapConnections registry value exists, you may want to delete this registry value to configure the Exchange server back to the default binary setting.

The Exchange Server Analyzer reports this configuration for informational purposes only. However, you may want to change the registry value back to the default setting by editing the registry.


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

To correct this warning

  1. Click Start, click Run, type Regedit, and then click OK.

  2. In the console tree, locate and then click the following registry key: HKEY_LOCAL_MACHINE System\CurrentControlSet\Services\SMTPSvc\Parameters

  3. In the details pane, right-click the MaxLdapConnections registry value. Change value data to 8.

  4. Optionally, in the details pane you can right-click the MaxLdapConnections registry value and then click Delete. Confirm the deletion of the registry value by clicking Yes in the dialog box.

  5. Restart the Exchange server.

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

For more information about editing the Microsoft Windows registry, see the following Microsoft Knowledge Base articles: