You should probably think carefully about bouncing e-mails. You've probably gotten a number of bounced messages you didn't write in the past due to viruses. Well you were probably as irritated deleting them as you are when you see spam, right? Bounced emails just add to the problem and clog already congested mail relays. 99.9% of spammers forge headers anyways, so you're not going to likely bounce to the right person.