As I understand it one of the infrastructural problems that used to enable spam was botnets blowing out ungodly amounts of mail over port 25. This doesn't happe

As I understand it one of the infrastructural problems that used to enable spam was botnets blowing out ungodly amounts of mail over port 25. This doesn't happen nearly as often as it did, because most ISP's blocked port 25 by default. (You have to call them up to get it unblocked.) And of course most email services whitelist each other instead of blacklists. Botnets can still take advantage of webmail through more sophisticated methods. Since spam is just a symptom of large scale botnets. (The majority of the web is currently a zombie in some botnet IIRC.) One way to reduce a lot of bad faith Internet behavior is to kill botnets.