We provide a model to study the effect of improving the quality of the filters that users use, and the increase of the cost of mailing spam messages, on the total number of messages that spammers send. We show that increasing the cost of mailing spam messages have the unequivocal effect of...

We study how the launching of a do-not-spam registry will affect the internet’s efficiency. We show that as long as the cost of sending spam messages is not high, having rich users (who have high-quality filters) join the registry has the desirable effect of lowering the number of spam...