"Charles Lindsey" <chl(_at_)clerew(_dot_)man(_dot_)ac(_dot_)uk> writes:
The scenario you need to consider is where A asserts a policy of "I
sign everything", and sends a correctly signed message to some mailing
list B.
B can (and should) check that the signature is good, and is consistent
with A's policy, etc. But then B add his standard mailing list
boilerplate "NOTE WELL ..." thus breaking A's signature. He then
signs the message again (as a 3rd party).
Now the ultimate recipients see A's signature (no longer good), plus
A's policy. So the message is on the face of it "suspicious". So what
is the recipient supposed to do? He is a member of the list, and is
happy to trust the list maintainer, and can check the 2nd
signature. But he is still receiving conflicting advice.
The only real solution to this problem is for B to add an
Authentication-Results header (see the Mail-Vet-Discuss mailing list),
and to incluide that header in is own signature. Maybe that is
veering off topic for this list, but at least there should be a
pointer to that sort of possibility.
If A had used 'l=' and assuming the boilerplate is added to end of the
message and that B does not change the headers (eg to add [listname] at
the start of Subject:) then A's and B's signatures should both
validate.
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