XFOR: Message Looping with Exchange Server on a Windows 2000 Domain Controller (260247)

SYMPTOMS

If Exchange Server 5.5 is installed on a Microsoft Windows 2000 domain controller, some Internet e-mail messages may loop if the following conditions are met:

The Windows 2000 domain is domain.com.
The Exchange Server Simple Mail Transfer Protocol (SMTP) site address is exchangedomain.com.
The domain domain.com does not have an MX record configured in DNS.
Exchange Server is configured to reroute all e-mail messages except e-mail messages to exchangedomain.com (set to deliver inbound).
A message is sent to domain.com.

The following events may be logged in the application event log:

Event ID: 4115
Event Type: Error
Event Source: MSExchangeIMC
Event Category: Internal Processing

Description:
The message from the spool file archivename seems to be looping through the routing extension for the Internet Mail Service. Please check that the routing DLL is configured properly.
Event ID: 12071
Event Type: Warning
Event Source: MSExchangeIS
Event Category: Content Engine

Description:
Message MessageID with subject subject of message from sender exceeded the maximum hop count(80040C02-8200008C). The archive filename is archivename.
Event ID: 4098
Event Type: Error
Event Source: MSExchangeIMC
Event Category: Internal Processing

Description:
The following message could not be delivered because the hop count exceeded the maximum. Check your configuration to make sure messages are not looping.
From: sender
Subject: subject of message

CAUSE

This behavior occurs because Internet Mail Service is connecting to itself in an attempt to deliver the message.

It is important to note that this is not a problem with either Exchange Server or Windows 2000. Refer to the "More Information" section of this article for further explanation of this behavior.

RESOLUTION

To resolve this problem, use one of the following methods:

Add an MX record for domain.com in DNS specifying the proper mail host.
Add domain.com in the Specify by E-Mail Domain area on the Connections tab of Internet Mail Service properties specifying the proper mail host.
On the Routing tab of Internet Mail Service, configure domain.com to route to the correct destination mail host.

NOTE: The first two methods are the best ways to resolve this issue. Although the third method prevents the message from looping, it still causes Internet Mail Service to first connect to itself to deliver the message and then reroutes the message to its intended destination.

MORE INFORMATION

When a Windows 2000 domain controller is created, it registers an A record for its Windows 2000 domain. In the situation described in this article, the Windows 2000 domain is domain.com.

NOTE: This domain should not be confused with the domain used for Internet mail. The domain domain.com specifies a security namespace, while the domain exchangedomain.com specifies a messaging namespace. The two namespaces are completely separate, and can have different names. Therefore an A record for domain.com is dynamically registered in DNS, and it points to the IP address of the domain controller.

When Internet Mail Service tries to deliver an SMTP message, the service first queries DNS for an MX record for the destination domain. If the query does not return an MX record for the destination domain, Internet Mail Service queries DNS for an A record for the destination domain. If an A record is returned, Internet Mail Service connects to the IP address specified in the A record and delivers the message.

In this situation, Internet Mail Service attempts to deliver the message to itself because of the following reasons:

The MX record query does not return any records because an MX record is not configured in DNS.
The A record query successfully finds the A record for the domain controller.