Authenticating Web users registered in a Microsoft Exchange Server directory fails if the Exchange Server the Domino Web server connects to is not a Primary Domain controller or a Backup Domain controller and the users belong to a different Windows NT domain than the Exchange Server. Authentication fails because in this situation the Exchange Server requires clients to bind using cn=NTAccount,cn=NTDomain while directory assistance requires that users' distinguished names -- the industry standard convention -- be used for binds. A workaround for this problem is making sure that the users and the Exchange Server reside in the same NT domain.