DOCUMENT:Q146126  14-MAR-1999  [exchange]
TITLE   :XFOR: Controlling IMC Loopback Connections
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, version 4.0 
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SUMMARY
=======

The Microsoft Exchange Internet Mail Connector (IMC) determines if messages are
being sent to the SMTP addresses that reside on the same site as the IMC. The
IMC can reject the message or send it to the Internet (depending on a Windows NT
Server registry setting). If the message is sent to the Internet, it is returned
to the Exchange system through the IMC. This process is inefficient, and it
affects the performance of the IMC. If the IMC rejects the message, the sender
receives the following "Non Delivery Report" message:

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


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

To disable the loopback messaging, do the following:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide
problems that may require you to reinstall Windows NT to correct them. Microsoft
cannot guarantee that any problems resulting from the use of Registry Editor can
be solved. Use this tool at your own risk.

1. Start Registry Editor (REGEDT32.EXE) and locate the following Registry subkey
   in the HKEY_LOCAL_MACHINE subtree:

   \SYSTEM\CurrentControlSet\Services\MSExchangeIMC\Parameters

2. From the Edit menu, select Add Value.

3. Enter the following:

      Value Name: DisableLoopbackConnections
      Data Type:  REG_DWORD
      String:     1 (Default is 0)

4. Choose OK and quit the Registry Editor.

5. Shut down and restart Windows NT.

Additional query words: imc win16 winnt win95

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Keywords          : kbusage 
Technology        : kbExchangeSearch kbExchange400 kbZNotKeyword2
Version           : 4.0 5.0

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