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Q234280: XCON: Increasing MTA Ability to Pass Mail over Slow Connections

Article: Q234280
Product(s): Microsoft Exchange
Version(s): 5.5
Operating System(s): 
Keyword(s): exc55
Last Modified: 06-AUG-2002

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The information in this article applies to:

- Microsoft Exchange Server, version 5.5 
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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:

  Q256986 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.

Additional query words: latency, RPC

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Keywords          : exc55 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : :5.5
Issue type        : kbhowto kbprb

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