not sending mail

[marlin]

I have installed round cube and am having trouble sending mail. I can recieve mail. I also have trouble sending mail with squirrelmail I get an error message with this as follows: '/usr/local/cpanel/bin/sendmail_cpanel -i -t -fmarlinj@rationaldata.net' I suspect that both programs are having the same problem. I have also disable spam assasin on the server because I read that there were some issues with this. Anyone have any ideas?