Proof of Work can Work.
Debin Liu, L. Jean Camp · WEIS · 2006
and Overview Proof of work has been proposed as a mechanism to increase the cost of email so that spamming is no longer economically attractive. However, the first economic examination of proof of work argued that POW would not, in fact, work because of the difference of cost to spammers and senders of legitimate email. We illustrate that this shift in the production frontier enabled by zombies does not remove the efficacy of proof of work if work requirements are weighted by a reputation function. We illustrate that proof of work can worked when combined with the currently used reputation systems in commercial anti-spam technologies.