On 2020-07-29 1:41 a.m., John R Levine (quoting Jesse) wrote: > >> I think that draft-kucherawy-dkim-transform-02 is getting at what >> I was originally thinking. In my opinion, MLMs will *always* need >> to munge, because they will never know if an arbitrary receiver >> will trust their non-munged mail. Giving the receivers a way to >> un-munge (if they can and/or want and/or trust) would be a >> productive path forward out of this situation.> > We already have a couple of ways to do reversible message munging, > starting with MIME message wrapping. In principle it works fine, in > practice it's awful because MUAs don't show wrapped messages > consistently and often in ways that are painful, e.g., you can see the > original author address but there's no button you can push to respond > to it. > > Unwrapping a MIME attachment is a lot easier than the proposed DKIM > unmunging but I doubt either is going to show up in MUAs any time > soon. Perhaps you could do it in a mail gateway.
Looking at the steps required to carry out the proposed unmunging, "a lot easier" doesn't seem to be an accurate measurement. Actually, reversing the tf=footer is simpler than unwrapping a message/rfc822 attachment.[*] The major difficulty is for MLMs to produce modifications that consist of the allowed transformations _only_. Perhaps, it is a lot easier to create a message/rfc822 without breaking its signatures...? From: rewriting in particular should be added to the set of allowed transforms. The MLM should make sure the Author: field mirrors the original From: exactly. Then it rewrites From:. It may seem redundant to set a tf= tag on the one hand and undo transforms on the other, since a munged From: is enough to pass. However, if receivers send aggregate reports back to the MLM, we can hope that one day they'll all succeed and the MLM can stop rewriting From:. In the interim, an MX which verified the original signature up to allowed transforms can replace the value of From: with that of Author:. This action is legitimate if all agree that the only reason why MLMs rewrite From: is to pass DMARC checking. I'd leave footers and subject tags in place. Best Ale -- [*] https://mailarchive.ietf.org/arch/msg/dmarc/2ZN7DS5NktoyEPItZ5vzr-xd0Mc _______________________________________________ dmarc mailing list [email protected] https://www.ietf.org/mailman/listinfo/dmarc
