DOCUMENT:Q230497  29-JUL-1999  [exchange]
TITLE   :XCON: MTA Sends NDR: Message Transfer Service Congestion
PRODUCT :Microsoft Exchange
PROD/VER:winnt:5.5
OPER/SYS:
KEYWORDS:exc55

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The information in this article applies to:

 - Microsoft Exchange Server, version 5.5 
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SYMPTOMS
========

This article applies to Exchange Server organizations using X.400 Connectors to
interconnect Exchange Server sites.

Users are reporting receiving non-delivery reports (NDRs) when they send messages
to certain Exchange Server sites. The NDR appears as follows:

   Your message did not reach some or all of the intended recipients.

   Subject: test 10:00
   Sent: 4/29/99 10:02 AM

   The following recipient(s) could not be reached:

   Doe, John on 4/29/99 10:17 AM
   The recipient could not be processed due to congestion in the message transfer
   service. The MTS-ID of the original message is:
   c=US;a=;p=DTF;l=NTMX17OA-990429140155Z-96516
   MSEXCH:MSExchangeMTA:HSD:NTMX21BE

The local Exchange Server bridgehead server may show the following events in the
application event log in regards to the non-delivery of messages:

   Event ID :290
   A non-delivery report (reason code transfer-failure and diagnostic code
   MTS-congestion) is being generated for message C=US;A=
   ;P=UTC;L=HSMX30NT-990429133235Z-1108. It was originally destined for
   DN:/o=UTC/ou=HSD/cn=Configuration/cn=Servers/cn=HSMX21NT/cn=Microsoft DSA
   (recipient number 1), and was to be redirected to
   DN:/o=UTC/ou=HSD/cn=CONFIGURATION/cn=SERVERS/cn=HSMX21NT/cn=MICROSOFT DSA
   C=US;A= ;P=UTC;O=HSD;S=HSMX21NT-DSA;. [MTA DISP:RESULT 22 136] (12)

CAUSE
=====

The message transfer service congestion NDR is sent when the user's local
bridgehead server has had consistent difficulty reaching a remote message
transfer agent (MTA) over an extended period of time. This can be caused by the
known issue mentioned in the following Microsoft Knowledge Base articles:

   Q193894 XCON: MTA Stops Processing Messages and Generates 9156 Events

   Q229643 XCON: 9156 Errors Occur after Applying Exchange 5.5 Service Pack 2

In brief, the Exchange Server MTA may run out of TCP/IP control blocks and then
can no longer initiate or accept X.400 communications from other MTAs.

RESOLUTION
==========

To verify whether an Exchange Server X.400 bridgehead server is out of TCP/IP
control blocks, examine the application log for the following event:

   Source: MSExchangeMTA
   Category: Resource
   Type: Warning:
   A resource limit has been reached while attempting to open an association.
   There are no free control blocks available for network type 1. The configured
   count is 20. [BASE IL TCP/IP DRVR 8 282] (10)

After the above event is logged in the application, the MTA cannot send or
receive messages to other MTAs. Unless there is another valid route for the
messages to be delivered to the remote Exchange Server site, the MTA is forced
to send NDRs for those messages after a period of time.

To immediately establish mail flow, the MTA logging the events needs to be
re-started. However, the long-term resolution is listed in Microsoft Knowledge
Base article Q229643.

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

Some Exchange Server organizations use only one route between Exchange Server
sites. In cases where that route is an X.400 Connector and the X.400 bridgehead
server MTAs are logging the 9156 events, the Exchange Server Directory service
cannot update the remote site's directory. The Directory service may log the
following events as evidence of the mail flow problems:

   Event ID: 1103
   Source: MSExchangeDS
   Category: Replication
   Type: Warning
   During intersite replication, the directory replication agent (DRA) received a
   non-delivery report (NDR) for messages submitted for the directory at
   Microsoft DSA. The diagnostic is 2. The reason is 0.

After mail flow is reestablished over the X.400 Connectors connecting the two
sites, the Exchange Server Directory service can send and receive directory
updates and no longer logs the above event.

Additional query words: mts

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

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Copyright Microsoft Corporation 1999.