Hi Raj and Mike, > My reply applies to OWA login not Outlook 2003. This is a problem I had > a few days ago, and solved it by applying SP2 for XP. When you logon to > OWA, you have to use the format domain\username to login, and > user@xxxxxxxxxx will not work. This is the problem I had, and fixed it > with SP2. Even if you specify \ as the default domain to authenticate in > IIS, that does not enable UPN authentication without the patch or SP2. I am not sure if the above applies to me, as this behavior also occurs on Windows 2000 Workstations. I am checking KB 830827 to see if it helps, thanks Mike! best regards Mike.