MTA Kernel threads parameter is non-default

[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 its current value:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeMTA\Parameters\Kernel threads

If the Exchange Server Analyzer finds the value for Kernel threads present and greater than 0 but set to anything other than 1 or 3, a non-default configuration message is displayed.

The Kernel threads value is the number of platform threads that handle the Presentation and Session level of the Open Systems Interconnection (OSI) stack. These threads are at the heart of message transfer agent (MTA) message processing. If this MTA communicates with many other Exchange Server version 5.5 servers using remote procedure call (RPC) over slow or highly latent network connections, it is recommended that you use a value listed in the following table.

Value Description

0x3 (hex)

Standard recommendation. Use this for any MTA that communicates with other Exchange Server 5.5 servers using RPC over slow or highly latent network connections.

0x8 (hex)

Use this for Exchange 2000 Server or Exchange Server 2003 MTAs that belong to a site containing more than 15 Exchange Server 5.5 computers.

0xC (hex)

Use this for Exchange 2000 Server or Exchange Server 2003 MTAs that belong to a site containing more than 30 Exchange Server 5.5 computers.


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 edit the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To configure the Kernel threads value

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

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeMTA\Parameters

  3. In the right pane, locate and double-click the Kernel threads value.

  4. In the Value data field, enter the value that is appropriate for your organization and click OK.

  5. Close the registry editor and then restart the Microsoft Exchange MTA Stacks service 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" (