>Accounting for how much spam actually reaches the inbox, we estimate that only about 1 in 25,000 people needs to succumb to the temptation to make a grey-market purchase to make it protable for spammers to inundate everyone with advertisements at current levels.

http://www.davidreiley.com/papers/SpamEconomics.pdf

Thanks for the link, that's a fascinating paper.

One thing that drives me nuts about that paper format (a LaTEX template, I guess) is that it doesn't have a date. And this happens a lot. If the topic was an abstract mathematical concept, evergreen and timeless, then the date isn't so important. But a paper about spam that is vague on the date? I don't understand. That field is always changing, and I presume the economics are changing, too.

This is rather typical, because when you prepare a paper you don't yet know the publication date, so your submitted/final version can't include any date, but the published version tends to be behind a paywall.

Published in February 2012, revised in June 2012, according to this:

http://www.davidreiley.com/papers/SpamEconomics.html