>As I recall this was considered during the development of DKIM originally, >exactly for this reason. We rejected it because we couldn't come up with a >safe description of what a tag should look like.
Yeah, that's what I recall, we couldn't figure out a way to allow benign modifications without also allowing spammy ones. Has anyone looked at my double signing draft? The idea is the the original sender (which we'll call, oh, Yahoo) puts on a very weak signature probably only on From, Date, and Message-ID, with l=0 and a new tag that says the signature is only valid if the message is also signed by a specific other domain, call it ietf.org. It probably also puts on an ordinary strong signature, too, and sends the message to a list forwarder such as [email protected]. The list does what it does, and signs the message normally with d=ietf.org. That breaks the strong yahoo signature, but the weak one is now valid in combination with the normal ietf.org signature, so there's a valid d=yahoo signature and DMARC is happy. The forwarder could of course do naughty things, but only the specific forwarder to whom the message was sent, which greatly limits the scope of damage. It's even more limited in the common case that the original sender has a reasonably good idea who are likely to be the well behaved forwarders and only puts the weak signatures on mail sent to them. R's, John _______________________________________________ dmarc mailing list [email protected] https://www.ietf.org/mailman/listinfo/dmarc
