MTA Max RPC calls outstanding 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\Max RPC Calls Outstanding

If the Exchange Server Analyzer finds the value for Max RPC Calls Outstanding present and set to anything other than 50, a non-default configuration message is displayed.

The Max RPC Calls Outstanding value is the maximum number of remote procedure call (RPC) threads. This limits the maximum number of RPCs that are guaranteed to be processed at one time. This value is used by RpcServerUseAllProtSeqs() and RpcServerListen().

In mixed-vintage scenarios where Exchange 2000 Server and/or Exchange Server 2003 coexists with Exchange Server version 5.5 computers and you have increased the number of Gateway In/Out threads in the Store.exe process, it is recommended that you increase the value data to 0x80 (hex) or 128 (decimal).


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\MSExchangeMTA\Parameters

  3. In the right pane, locate and double-click the Max RPC Calls Outstanding value.

  4. In the Value data field, enter 50 and click OK.

  5. Exit the registry editor and 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" (