When attempting to send mail using my E-Smith 6b3 mail server, I get this error (personal info removed just because

):
The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'bleh@nowhere.net'. Subject 'test', Account: 'mail.***.net', Server: 'mail.***.net', Protocol: SMTP, Server Response: '553 Sorry, that domain isn't in my list of allowed rcpthosts.', Port: 25, Secure(SSL): No, Server Error: 553, Error Number: 0x800CCC79
The pop server works just fine, it is only sending mail I'm having problems with.
What does this mean, is my SMTP not working correctly? Any ideas on how I can fix this?
Thanks guys!