How to Set the TCP/IP Control Blocks Registry Value

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The TCP/IP control blocks registry value is the maximum number of concurrent RFC1006 (TCP/IP) connections that are supported. This setting controls the number of buffers available for X.400 connections. If this message transfer agent (MTA) hosts more than one X.400 connector, the TCP/IP control blocks registry value should be adjusted. There should be 10 control blocks for each X.400 connector being hosted, and one control block to service incoming connections. Therefore, for a system with three X.400 connections, the appropriate value would be 33.

In smaller organizations, the MTA process typically does not require manual tuning. After you have converted to Native Mode, you should remove these registry settings. Using the MTA tuning described below in a Native Mode Exchange organization decreases the performance of Exchange.

Before You Begin

Before you perform the procedure in this topic, be aware that the procedure contains information about editing the registry.

Warning

Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

Procedure

To set the TCP/IP control blocks registry 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 TCP/IP control blocks.

  4. In the Value data field, enter the appropriate value and click OK.

  5. Close the registry editor and restart the Microsoft Exchange MTA Stacks service for the change to take effect.

For More Information

For information about how to edit the registry, see Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=256986).