Why can't i send to this list

Hi Im have big problems sending to this list, from mutt and my other email addres i can't get any mail to this list, i get a error 67 unknown user why is that, is my sendmail configuret wrong or what i can send to everyone else but this list, now im trying from kmail to see if it helps ? Tia -- Best regards/Med venlig hilsen Dan Christensen icq# 2778293 Powered by SuSE Linux 8.0 Professional