Prevent Server From Sending Spam

My server keeps getting flagged for sending spam. If I check /var/spool/mequeue I can see hundreds of spam emails. I need somebody to: Figure out what scripts are causing this spam email. Help me configure the server so that only domains on the server can send mail, not external domains. Answer my questions. I need this done immediately, so please do not bid if you cannot do this right now. The lowest bidder is most likely to win.