The reports I can pull include a report on traffic by recipient, which includes email addressed to accounts that don’t exist. The woman who used to be listed as our website’s contact when you did a Whois search hasn’t worked here in almost 4 years. Her address was last accesible by doing a Whois more than 3 years ago. There have been over 800 emails addressed to her that came in this last week. Her email address has been undeliverable for almost 4 years, yet she still gets more spam than anyone else here who’s address is active. This shows me two things:
One, that Whois information, at least before safeguards were put in place, was a popular place to collect addresses for spammers.
Two, that bouncing emails for bad addresses has no effect whatsoever on stopping spam.