XCON: Mail Flow Stalled in MTA Queue, Events 9316, 9318 Appear

ID: Q253304

The information in this article applies to:
  • Microsoft Exchange Server, versions 5.5, 5.5 SP2
IMPORTANT: 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 "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SYMPTOMS

When you administer Exchange Server, you may find that mail is backing up in multiple servers within a site, or over a site connector, and that the message transfer agent (MTA) appears to be stalled.

The application log of Event Viewer displays the following events:

Event ID: 9318
Source: MSExchangeMTA
Description: An RPC communications error occurred. Unable to bind over RPC. The locality table (LTAB) index is 76. Windows NT error code: X [BASE IL MAIN BASE 1 500] (12)

Event ID: 9316
Source: MTA
Description: An RPC communications error occurred. No data was sent over the RPC connection. Locality table (LTAB) index: 4. Windows NT error: X. The MTA will attempt to recover the RPC connection. [BASE IL PIPE RAS 24 230] (12)
When you test remote procedure call (RPC) connections using the RPC PING utility, you find no problems. When you check the Calls.out file, you discover that there are stalled threads. Restarting the Exchange Server computer does not correct the problem, and the MTACheck utility does not document any errors.


CAUSE

This behavior can occur when your local area network (LAN) speed is low, when you use LAN high latency site connectors, or when there is heavy network traffic. Typically, this behavior occurs on Exchange Server computers where the MTA is highly stressed. Frequently, but not exclusively, Exchange Server 5.5 SP 2 installed on a computer running Microsoft Windows NT Server 4.0 Service Pack 4 exhibits this behavior.


RESOLUTION

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).


To resolve this behavior, upgrade to a faster LAN if all of the Exchange Server computers are within a single site, or use TCP/IP when you are working with multiple sites.

As a workaround in case neither of these alternatives is possible, increase MTA thread values in the registry. Follow these steps:

  1. Stop the MTA if it is still running.


  2. Increase the relevant thread values in the registry:


    1. Start Registry Editor (Regedt32.exe).


    2. Locate the RTS value under the following key in the registry:


      3. 
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeMTA\Parameters
    3. Double-click RTS, and then type 8 in the box. This sets the value data to 0x8.


    4. Click OK.


    5. Perform the same procedure for each of these other values:


      6. Kernel threads

      Dispatcher threads

      Transfer threads
    6. Quit Registry Editor.


  3. Restart the MTA.



MORE INFORMATION

Kernel threads are Open Systems Interconnect (OSI) Stack thread calls. Kernel threads represent the number of platform threads handling the Presentation and Session level of the OSI stack.

RTS threads are also OSI stack thread calls. They represent the number of platform threads handling the reliable transfer service element (RTSE) level of the OSI stack.

Dispatcher threads handle all of the routing, fanout, and result functions. Be aware that increasing this number actually increases the thread count by three, one for each of the dispatch functions mentioned here.

Transfer threads act in much the same way as submit/deliver threads but do so for gateways and MTAs. On a bridgehead server whose MTA has no local users, there is effectively no information store. In this case, you can improve performance if you set the submit/deliver threads to the lowest value, 1, and then increase transfer threads to a higher number to handle the relaying and gateway interactions.

When low bandwidth or high latency site connectors cause bottlenecks, modifying the kernel threads can improve the situation. However, the best solution is to upgrade to a faster LAN if all the Exchange Server computers are within a site, or use TCP/IP connections between sites. Thread pools are limited, and thus modifying threads is only a workaround rather than a solution.

For additional information on generating a Calls.out file, click the article number below to view the article in the Microsoft Knowledge Base:

Q178531 Generating the Calls.out File

Additional query words:

Keywords :
Version : winnt:5.5,5.5 SP2
Platform : winnt
Issue type : kbprb


Last Reviewed: February 3, 2000
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