XFOR: Controlling IMC Loopback Connections

• Microsoft Exchange Server, version 4.0

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.