It doesn't have anything inherent to do with the user's From address
The way the wind seems to be blowing, SPF will change that during the
next year or two. For better or worse.
I hope you're wrong. Because if there's anything worse than spammers, it's
people who try to impose half-baked solutions to spam on the rest of ous.
I doubt very very much he's wrong. We may not end up with SPF exactly, but I
think it is inevitable that one of these critters is going to widely deploy and
compromise various existing facilities.
In fact my worst fear could easily be realized, which is that multiple,
incompatible schems of this sort will deploy. Figuring out how to keep
forwarding working with one of these is bad enough, making it work with more
than one of these things, especially if the requirements they impose conflict
in some way, doesn't bear thinking about.
This is why there's going to be a BOF (MARID) on this in Korea - we REALLY need
to get a handle on the situation.