I don't see why we should help anyone sending mail from a
dynamic IP. _Most_ people on dynamic IP's are not capable
of running MTA's.
Like Will said - there's no way to tell what is or is not a dynamic IP
(and especially not with any reliability strong enough to use such
3rd party guesswork as a rule for erasing other peoples emails!) so
this whole debate is pointless.
ISPs themselves know their dynamic's, so they can set up their SPF
records accordingly, so the problem is fixed by the only people who
actually do know what is dynamic - that's *exactly* what SPF is *for*.
Remember that Kiwi RBL idiot who added some people into his RBL simply
out of spite? He's not the only one who does this - but he did get
sued, lost, and had all his assets confiscated to pay damages, which
included his house. There's a really simple lesson to be learned
here: "Be nice to people".