Configuring NTLMv1 and NTLMv2 compatibility for Outlook 2003 and Windows XP SP2
In Windows XP SP2, Outlook 2003 email windows other than the preview pane may not pass NTLM credentials transparently. If a user opens a message that contains embedded HTML and the user is not currently authenticated, an authentication dialog box is displayed. To prevent the dialog box, get Windows XP SP3 or a hot fix and modify the registry. These changes must be made to every user computer.
To modify Windows XP to support transparent NTLM authentication with Outlook 2003
Do one of the following:
Request hot fix 895948 from Microsoft.
Install Windows XP SP3, which contains hot fix 895948.
To modify the registry to support transparent NTLM authentication with Outlook 2003
In Windows, click Start > Run, type regedit, and click OK.