"John" == John R Levine <johnl(_at_)iecc(_dot_)com> writes:
John> This is the Project Lumos fallacy. I have no interest whatsoever in
John> distinguishing between a domain's nice users and its nasty users. I
John> believe that each domain is responsible for keeping its users in
line, and
John> the reason that signatures are useful is to help me alert domains
about
John> undesirable mail they've sent. If they send a lot of undesirable
mail,
John> I'm going to reject the whole domain, not do their filtering for them.
As discussed in section 4.1 of Russ's draft, a domain cannot know how
widely a message will be distributed. Once I have a signed copy of
that message I can choose to distribute it much more widely than the
sending domain might like me to do.
Fundamentally what you are asking for is incompatible with ISPs that
will provide service to users until those users violate the terms of
service. The user can take one action--signing one message and widely
distribute that signed message.
For a large ISP this will happen enough that your strategy will end up
deciding all the large isps have unacceptable reputations.