Microsoft KB Archive/168090

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Last reviewed: December 16, 1997

Article ID: Q168090 The information in this article applies to:
 * Microsoft Exchange Server versions 4.0 and 5.0

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information on how to do this, view the "Restoring the Registry" online Help topic in Regedit.exe or the "Restoring a Registry Key" online Help topic in Regedt32.exe.

SYMPTOMS
This problem occurs when you send SMTP messages through the Internet Mail Connector (IMC) (or Internet Mail Service [IMS] in version 5.0) to domains with multiple MX records. The messages stay in the outbound queue awaiting delivery, get name resolution, then time out, and a non-delivery report (NDR) is delivered. This problem is usually encountered when you send SMTP messages to large corporations.

The following error message may be received when getting information on the message's setting in the queue:

421 NSO hq.com Unable to contact destination SMTP demon nestle.com The computer running Microsoft Exchange Server is able to Telnet to these servers, and is able to send to any other domains.

WORKAROUND
WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall Windows. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" online Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" online Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

To work around this problem:

 Start Registry Editor (Regedt32.exe or Regedit.exe as appropriate for your version of Windows NT).  Go to the following key in the registry: HKEY_LOCAL_MACHINE\System\CCS\Services\MSExchangeIMC\Parameters   On the Edit menu, click Add Value and use the following entry: Value Name: DisableResolverSearchList Data Type: REG_DWORD Value: 1 (or any non-zero value)  Exit Registry Editor. Use NSLookup to get the correct IP addresses for the correct MX records of each e-mail domain. In the IMC or IMS Connections tab, click the E-Mail Domain command to specify Message Delivery by E-Mail domain. Type one domain name/IP address pair for every MX record found in step 5. Repeat steps 6 and 7 for every other domain that has multiple MX records and is facing this problem.</li> Send a message to each one of these domains to test the workaround.</li></ol>

MORE INFORMATION
When you are having this problem, a Traceroute to these domains is successful.

SMTP protocol log for a failed connection may show that the IMC made a connection but the mailer demon never responded to the connection.
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