Perhaps an analogy from a different but familiar world will help.
Consider DKIM or SSP as broadcast radio transmissions (or TV if
you must). The point is that it is a UNIDIRECTIONAL thing. The
sender doesn't know if anyone is receiving the signal, and they
certainly can't force anyone to listen (or watch their TV program).
Likewise, the sender of DKIM-enabled email doesn't know if the
receiver implements DKIM or SSP, and they certainly can't force
them to implement unenforceable statements that say "deny".
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.
Wietse
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