XIMS: AUTH LOGIN Command Must Use Base-64-Encoded User Name and Password (235627)

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SUMMARY

Microsoft Exchange Server 5.5 supports the AUTH LOGIN command for clear text authentication using a base-64-encoded user name and password. It does not accept the AUTH LOGIN command if the user name and password are in an X.500 Distinguished Name (DN) format. If the AUTH LOGIN command is sent in this manner, the following event may appear in the event log on the Exchange Server computer, indicating that the authentication attempt was not successful:

Event ID: 4183
Description: Authentication attempt (AUTH LOGIN) from hostname as username failed: LogonUser() call failed with error: Logon failure: unknown user name or bad password.

Note that when responding to an EHLO command, Exchange Server always indicates that it supports the AUTH LOGIN command.

MORE INFORMATION

Microsoft recognizes the fact that some e-mail clients and servers send the AUTH LOGIN command with a user name and password in an X.500 DN format. We have modified the Internet Mail Service so it can be configured to behave in the following manner:

AUTH commands are not accepted by the server.
When responding to an EHLO command, the server does not indicate that it supports the AUTH LOGIN command.

This feature is available in the latest service pack for Exchange Server version 5.5. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

191014 XGEN: How to Obtain the Latest Exchange Server 5.5 Service Pack

The English version of this feature should have the following file attributes or later:

Component: Internet Mail Service

File name	Version
Imcmsg.dll	5.5.2638.0
Msexcimc.exe	5.5.2638.0

This feature was first included in Exchange Server 5.5 Service Pack 3. After you obtain this feature, to modify the behavior of the Internet Mail Service:

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

Start Registry Editor (Regedt32.exe).
Locate the following key in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIMC\Parameters
NOTE: The above registry key is one path; it has been wrapped for readability.
On the Edit menu, click Add Value, and then add the following registry value:
Value Name: DisableAuth
Data Type: REG_DWORD
Value: 1 (or any other non-zero value)
Quit Registry Editor.