According to MS, http://support.microsoft.com/default.aspx?scid=kb;en-us;260832&Product=exch2003 you cannot access Exchange 5.5 mailboxes using OWA 2003. However, this article seems to state it is backwards compatible. http://www.msexchange.org/tutorials/Migrating_Exchange_5_5_to_2003.html "Replacing your existing OWA Front-End Server will be very easy, because the new release will provide backward compatibility with Exchange Server 2000 and 5.5. The new look of Outlook Web Access will be provided to each user, if both ? back and front-ends are on Exchange Server 2003." However, it seems somewhat contradictory. Anyone have this working?