DOCUMENT:Q169691  02-MAY-1999  [exchange]
TITLE   :XCON: MTA Slow to X.400 Links
PRODUCT :Microsoft Exchange
PROD/VER:4.0 5.0
OPER/SYS:
KEYWORDS:kbusage

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The information in this article applies to:

 - Microsoft Exchange Server, versions 4.0, 5.0 
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SYMPTOMS
========

The Microsoft Exchange Server message transfer agent (MTA) delivers mail
extremely slowly on computers that have multiple X.400 links over TCP/IP if some
of the TCP/IP connections are over slow network links.

CAUSE
=====

Flow control within the MTA code above the WINSOCK layer (within the TP0
Transport layer for TCP/IP or Session layer for TP4) for the slowest connection
is stalling mail for faster connections.

STATUS
======

Microsoft has confirmed this to be a problem in Microsoft Exchange Server
version 4.0. This problem has been corrected in the latest U.S. Service Pack for
Microsoft Exchange Server version 4.0. For information on obtaining the Service
Pack, query on the following word in the Microsoft Knowledge Base (without the
spaces):

   S E R V P A C K

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version
5.0. This problem has been corrected in the latest U.S. Service Pack for
Microsoft Exchange Server version 5.0. For information on obtaining the service
pack, query on the following word in the Microsoft Knowledge Base (without the
spaces):

   S E R V P A C K

MORE INFORMATION
================

With the fix applied, the MTA changes the flow control method within the OSI
stack above the TCP/IP (or TP4) connection to allow WinSock to handle flow
control. This will make the X.400 links faster because WinSock is multithreaded
and can handle as much as the MTA can hand to it.

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Keywords          : kbusage 
Technology        : kbExchangeSearch kbExchange500 kbExchange400 kbZNotKeyword2
Version           : 4.0 5.0
Issue type        : kbbug
Solution Type     : kbfix

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Copyright Microsoft Corporation 1999.