Mark Sapiro writes:
They would just add the one line
SENDER_HEADERS = (None, 'from', 'reply-to', 'sender')
An alternative to this would be a custom pipeline with the places that checks SENDER_HEADERS altered to use that. You might also want to grep for some appropriate host's trace headers to avoid replay attacks.
Sorry, I don't have time to go into detail, but I think that in combination with changing the list-post address to go directly to the moderator should do what Bill wants to happen. It has the big advantage from the host's point of view that it only affects Bill's list; the small disadvantage is a small amount of work installing the change.
It's not a ton of work though; the first time I did this it took 45 minutes from deciding to do it to a working installation. I think the host should be able to do this in less than 10 minutes, as long as Bill is willing to accept the slight risk that the ML might go down until the host has time to look at it again.