When you use Microsoft Outlook or Microsoft Outlook Express to try to log on to an HTTP-based mail server, authentication fails. This problem occurs when the following conditions are true:
The client computer that you use to try to log on to has Windows Internet Explorer 7 or Windows Internet Explorer 8 installed.
The HTTP server is using digest authentication.
This problem occurs because of changes in Internet Explorer 7 and in Internet Explorer 8.
To resolve this problem, use one of the following methods, depending on the version of Windows that you are using.
Note To determine which version of Windows that you are using, click Start, click Run, type winver, and then click OK.
To get the stand-alone package for this update, go to the Microsoft Update Catalog website.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.