Spammers do tend to use botnets these days but ISPs would love it if you sent reports to their abuse teams. Each ISP can help clean up bots on their network and while it is basically an endless game of whac-a-mole it does have an impact on the spam volumes leaving respectable networks. If you can automate the process of sending off a notice to the abuse team in addition to any other filter/drops it would be a win/win for everyone.
ARF is great, but as long the message includes the full message headers it should be possible for the ISP to track down the infected user responsible.
ARF is great, but as long the message includes the full message headers it should be possible for the ISP to track down the infected user responsible.