It appears that Michael Thomas via NANOG <nanog@lists.nanog.org> said:
Since this is a network operator list, here's my question. What percentage of traffic is spam? That is, total traffic? My guess is that it's minuscule. That and how negatively does it cut into bottom line for an operator like an ISP? I hardly see ISP based email anymore these days.
In terms of percentage of total bits, I'm sure you're right. Mail is a sliver of bandwidth, spam is between half and 90% of that. The problems are on the one hand, having a mailbox full of spam makes mail less useful (I am so tired of my morning B2B blasts from Outlook and Gmail), but on the other a lot of is linked to real crime with significant financial consequences to the victims. I agree that the incentives are skewed, with little incentive for ISPs to deal with it. I note that Comcast who used to run a large mail system recently handed it all over to Yahoo, presumably because Yahoo has economies of scale they don't. R's, John