Hm... let me try this
(with apologies for apparent abuse and delay)
Actually we need to validate two assertions:
* That the mail came from the stated author, e.g. PHB.
* That the mail was relayed by the IETF mailing list.
Well, yes, but those are easy.
Are they? If you can read this, then the first bullet was not applied, however
easy doing so would have been.
What's hard is demonstrating that the message
that the list relayed is the same in a semantic sense as the message that
Phill
sent, even though it has the kind of changes that lists make, a tag in the
subject line, a footer at the bottom, and attachments stripped.
That's hard indeed. We're probably better off just trusting the verified
sender identity (second bullet). The author could have vouched the sender with
a conditional signature...
Ale