Once a mailing list has been poisoned with a number of invalid e-mail addresses, the resources required to send a message to this list has increased, even though the number of valid recipients has not. If one can poison a spammer's mailing list, one can force the spammer to exhaust more resources to send e-mail, in theory costing the spammer money and time.[ 1]
Poisoning spammers' mailing lists is usually done by blacklists submitting fake information to email submit style offers, or by posting invalid email addresses in a Usenet forum or on a web page where spammers are believed to harvest email addresses for their mailing lists.