Article ID: 306874 - View products that this article applies to.
This article was previously published under Q306874
In a front-end and back-end environment, an Internet Message Access Protocol, Version 4rev1 (IMAP4) or Post Office Protocol version 3 (POP3) client (such as Microsoft Outlook Express) may not be able to authenticate logon credentials with the front-end server by using NTLM (or SPA). The client may prompt for authentication continuously.
Front-end servers do not support NTLM authentication because it requires a persistent connection. The front-end servers reuse connections as necessary. However, basic authentication is supported.
When you use Exchange 2000, this problem can occur because front-end IMAP4 or POP3 servers incorrectly advertise NTLM authentication. Exchange 2000 Service Pack 1 does not advertise NTLM, which allows the client program to indicate that the authentication is not supported or did not work. Installing Exchange 2000 Service Pack 1 does not change this aspect of the behavior of back-end servers.
To resolve this problem, obtain the latest service pack for Microsoft Exchange 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/301378/EN-US/ )XGEN: How to Obtain the Latest Exchange 2000 Server Service Pack
Microsoft has confirmed that this is a problem in Microsoft Exchange 2000 Server. This problem was first corrected in Microsoft Exchange 2000 Service Pack 1.
You can test the behavior difference between an Exchange 2000 server and a server on which Exchange 2000 Service Pack 1 is applied. To do so, use the telnet utility: