John,
Yes, of course. The signature means that this message really truly
came from the mailing list, as opposed to being a random piece of spam
that happened to resemble list mail. What else would it mean? Lists
have never promised that the original sender was "real" nor that
messages aren't edited on the way through.
Lists never have had DKIM to deal with, so they've never had the option
to make any such promise. The signature lends the MLM's credibility to
the message, which in turn could hurt the MLM's credibility if it turns
out to be signing garbage. How else would a reputation for signers work?
The MLM wants to signal to the recipient the veracity of the origon.
That's why Murray's approach in the draft is to add an A-R header, which
he states in the draft goes beyond A-R's intent in terms of trust. An
alternative would be to simply not sign the message.
Eliot
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