Squirrelmail Changing Domain Name


I am running OS X 10.3.9 server. I have set up our email accounts and website on this server. Everything is working fine except for web mail. My we mail account works fine but all the others do not. They can receive eamil while in web mail but when they send it changes the domain name to our website.
so mine is robert@mbl-arch.com but when sending via web mail
it shows up as robert@www.mbl-arch.com. Then i checked it from within the office and it will change the www.mbl-arch.com
to the IP address of the computer i am at. Do you have any idea
what is wrong? I am going to look at my smtp settings but i have compared the account that works to the others and i can't see any difference. I know their is somthing i am missing. I would appreciate any help you could give me. Thanks...