Email not being sent

[techspec]

Following 2 re-installs of SBS2003 on my Dell 400SC server none of the workstations on our network are able to send emails via Exchange server.
The error message that keeps coming up is:-
"553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)"
I'm pretty sure this is just a setup issue but having searched several other forums there seems to be several opinions as to the cause of this error.
Any suggestions would be greatly appreciated.
All the workstations are running XP Pro (SP2) and using Outlook 2003 for email. :blackeye:

 

[sifugreg]

Normally this would be an incorrect DNS configuration on a Windows Server. Check your event viewer. If there are DNS errors, you may want to resolve those first. If you DNS is clean, you still may want to use the IP address of your Mail Server instead of the domain name. Additionally, something I've run into in the past is some ISP's only allow sending of mail within so many seconds of POP3 authentication. I believe QWest does this. This is their way of preventing relaying but it screwed me up seeing how they provide our connectivity but my POP3 email is with another company that houses our domain so I never downloaded POP3 from Qwest. It could be that username and password authentication are required to get around this. I'm not sure where that setting is but I'll try to remember to look on my server at work tomorrow. If I find anything good, I'll let you know.