Let's apply some analysis here. Would this fix be any worse than the
policy changes you instituted as a result of getting listed in ORBS?
In retrospect, was that change so dramatic that you would reverse it,
given the chance to do so?
ORBS just tried to close down open relays; they didn't try to force
users to submit mail from specific hosts.
First of all, you didn't answer the question.
that's because your question misses the point.
Secondly, your non-answer is somewhat misleading, since ORBS et al are
very much intent on preventing submissions from specific hosts, which is
in the same general category as this approach (secondary difference is
that this one is voluntary).
I'll grant that the ORBS approach suffers from the same kind of naivete.
Keith