I have recently join an environment that is not documented well. First problem, my account has been created, in local domain and email setup in MS Exchange 2003 running on Windows SBS. The account is able to send emails outside of the organzation without any problems. However, when sending emails from an external account to this account I receive Recipient unknow 5126.96.36.199 User Unknown error message. Old users work fine but I have created a couple of new users with the same problem. There are no more remaining IS individuals from the original group :-( so any assistance would be great. I can answer any questions about the setup. So far everything on the surface looks correct.