If your NT user name and Exchange2k email alias are not the same, you will not be able to log in to the Exchange 2k server via the internet with Outlook Express, Outlook, or similar client. Prior to Exch sp2, I could log in via Outlook Express over the internet to access mail on Exchange server using "fnamelname@sub.domain.com" with an email address of "fname.lname@domain.com". After SP2 this no longer works, see MSKB Q296387 for details. The NT Domain user name and email alias MUST be the same or you need to login with the format PRE2KDOM\USERNAME\EMAILALIAS. I hope this helps someone else - it drove me nuts for a while.