XCON: How to Increase the Ability of the MTA to Pass Mail over Slow Network Connections (234280)


The information in this article applies to:

  • Microsoft Exchange Server 5.5
This article was previously published under Q234280
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SUMMARY

Mail may process slowly or sporadically to other servers in the site across a site connector or over an X.400 Connector. You can view this mail in the Exchange Server Administrator program by opening the Properties of the Server object's Message Transfer Agent (MTA), and then clicking the Queues tab. You can also view this mail in Performance Monitor by viewing the following counters:

Object: MSExchangeMTA Connections
Counter: Queue Length
Instances: queues

MTA processor usage may be quite low, despite mail sitting in the queue.

MORE INFORMATION

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

There are certain MTA registry parameters that you can tune to increase the ability of the MTA to process mail over high latency or slow network connections. These registry locations are found in the registry by default. Run Registry Editor (Regedt32.exe) and go to the following key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeMTA\Parameters

The following values can be set from their default threads values of 1 to 3 to a higher value, such as 6 or 8. You must restart the MTA service for these changes to take effect.
  • Dispatcher threads: The number of MTA dispatcher threads. This is multiplied by three for the three subtypes (Router, Fanout, and Result) of dispatcher threads. Be aware that a change in this number actually increases the thread count by three, one for each of the Dispatch functions mentioned below.
    • Router - Routes messages.
    • Fanout - Sends message to the right place. For example, if a message has 10 recipients with 5 remote and 5 local, the fanout thread sends one copy to the information store and another copy to another MTA.
    • Result - Thread handles for notifications. For example, non-delivery reports (NDRs).
  • Kernel threads: These are Open Systems Interconnection (OSI) stack thread calls. You can alleviate bottlenecks caused by low bandwidth or high latency site local area network (LAN) connectors by increasing the Kernel threads value. A better solution, if it is possible, is to get a faster LAN within a site, or use TCP/IP connections such as X.400 Connectors between sites. The Kernel threads value represents the number of platform threads handling the Presentation and Session level of the OSI stack.
  • RTS (Reliable Transfer Service) threads: Number of platform threads handling the Reliable Transfer Service Element (RTSE) level of the OSI stack. The OSI stack is the stack that X.400 Connectors use.
  • Transfer threads: This is the equivalent of the Submit/Deliver threads value (which relates to MTA and information store message transfer) but for gateways and MTAs. This value is multiplied by two for the two subtypes (Transfer In, Transfer Out) of Transfer threads.
Modification Type:MinorLast Reviewed:4/28/2005
Keywords:kbhowto kbprb KB234280
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