unwanted mail..what can I do?

I recieved mail from netfree.com.. I tried mailing it back (it def. had a forged address, but I got the netfree from the mail header.....) So anyway..... I tried sending to root@netfree....my mail was rejected (not unknown ...it was rejected by the system) said it wasnt authorized... so I tried support@netfree...same thing. It ISSSSS rather annoying...any sugestions?