In part, the issue is being addressed in draft-ietf-dkim-mailinglists
already. I'm questioning whether we can get away with saying that a
MLM "is /likely/ to invalidate any or all of" a message's signatures.
Reputation considerations suggest that author domains may want MLMs
to behave consistently in this respect.
They may want that, but if we're documenting what MLMs do, I don't think
they can have what they want. The conditions under which an MLM will
break a signature are very hard to describe.
As a typical example, many MLMs add a subject line tag, but if the tag is
already present it leaves the line alone. So one message might arrive
with a broken signature, and the next, a response to the first message
which already has the tag in its subject line, might arrive with a valid
signature.
So "is likely to invalidate" is as specific as we can reasonably be.
R's,
John
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