XCON: MTA Sends NDRs Because of Message Transfer Service Congestion

ID: Q230497

The information in this article applies to:

Microsoft Exchange Server, version 5.5

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

Keywords : exc55
Version : winnt:5.5
Platform : winnt
Issue type : kbprb