Reddit - I need some help, and fast

I'm runnig debian/postfix(mysql)/apache, and it seems as though my server (linode) is sending spam like crazy. I've been told that it should be a simple config issue, but I don't know enough to sort it out. They have told me that if it's not fixed asap, they will shut down my server. Is there anyone out there who can help me out a bit, I don't mind paying for the help, I just need it fixed quick!