Wietse analogized:
DKIM and SSP have no more "enforcement" power than broadcast radio.
You don't know who "receives" the signal and you certainy can't force
them to do anything with it.
With the DKIM and SSP broadcast model, you can define the format of
the
signal and its meaning. That's all. If you want to control the
receiver
and "deny" mail, then you need a fundamentally different model.
The same could be said about email today, yet there's an entire industry
built up around senders of email trying to convince receiving sites to
treat their messages in particular ways. Senders of email /want/
certainty, and what we've seen so far is that they'll leap on even the
slightest hint that they're about to get it. SSP will be no different.
On the other side, many potential implementors really really want to
know that they can reject all unsigned mail from a particular domain.
Seems to me that that's the important part here. I'm not sure anything
else is going to matter.
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