Well, uh, we can just say "no" to them, then.
Personally, I assume that anything I write to any mailing list is likely to be archived permanently in places that are out of my control. So long as my mailings are not dishonestly altered, I don't care. Why should I care?
I have no idea if our software respects or passes along no-archiving headers. We're using standard open source software, so if there's a standard for this, it probably works just fine.
--Jimbo