the value in having the list processor sign all posts
is simple. guaranteed identification of the list
traffic for any recipient who decides to verify
signatures.
This seems to solve a non-problem. Unless there are spam messages that
where the sender has, for instance, forged the existing "Sender:
owner-ietf(_at_)ietf(_dot_)org" header, signing these messages will add nothing
of
value. It seems much more likely that a spammer would simply send e-mail to
the ietf(_at_)ietf(_dot_)org list & allow the list itself to propagate it than
that
they would specifically forge that header.