MTA stops processing messages and generates 9156 events

When a network connection goes down and the message transfer agent (MTA) is unable to send mail over an X.400 connector, the MTA leaks 1 CB if the number of connection attempts issued is more than 1. Eventually, the MTA will report 9156 errors in the application event log and a backlog of messages will begin to build.

This problem is caused by a bug in the MTA Winsock code.

Exchange Server 5.0

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next P1 that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Exchange Server 5.5

To resolve this problem, obtain the latest service pack for Exchange Server version 5.5. For more information, click the following article number to view the article in the Microsoft Knowledge Base: The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

If you are not able to install the latest hotfix or service pack, perform the following steps on the bridgehead servers logging the 9156 events, and on the remote X.400 bridgehead servers.:

1. Increase the TCP/IP control blocks in the registry located in the following key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeMTA\Parameters
   To do this, use the following equation:
   
   Edit the value of the TCP/IP control blocks so that it is equal to (10 * the number of X.400 connectors) + (number of sites).
   
   The results should be placed in the key as decimal.
2. On the Override property page of every X.400 connector, in the Associations section, increase the Disconnect value. The default is 120; increase the value to at least 360. This value can be increased or decreased as necessary to work around the problem.