On 7/6/20 10:41 AM, John R Levine wrote: > On Mon, 6 Jul 2020, Dave Crocker wrote: >>> I don't understand this scenario at all. Why would I want to show >>> my user a message forwarded by a spammer? If the original sender >>> wanted me to see it, she could have sent it to me directly, or >>> through a legit mailing list. >> >> Perhaps, like some others, I'm not understanding this correctly, but >> I think the proposal has nothing at all to do with what the recipient >> sees. Rather, I've understood this as an attempt to reverse >> additions made by a Mediator, with the goal of validating the >> origination DKIM signature. Presumably that is so as to use the >> origination domain's reputation and even permit DMARC to validate. > > But why would I want to do that? ARC lets a credible mediator say > this message was OK before I munged it. This proposal lets a sleazy > mediator say the same thing, with advice on how to verify mechanically.
Your use of "credible mediator" and "sleazy mediator" emphasizes that we're depending on the mediator behaving responsibly. Given that's the case, why not just expect a responsible mediator to verify the DKIM signature (or maybe SPF) on the incoming message, check its alignment with the From: domain, then make whatever modifications it wants to make, then re-sign the message with the mediator's DKIM signature containing a tag that says it did all of the above? Yes, this is a "get out of DMARC free" card for mediators to use. But we're already dependent on being able to distinguish between credible mediators and sleazy mediators, and this tag simply says, "if you trust that I'm a credible mediator and this message has a valid signature from me, you should accept the message even if my signature doesn't align with the From: domain." This gets us out of the business of trying to define what acceptable and unacceptable transformations are. If the transformation was done by a credible mediator, it's acceptable. Many (most?) mediators do not currently require authentication (+alignment) on incoming messages. They could continue to forward the unauthenticated messages, but without the new tag. -Jim P.S. I'm still not sold on the value of From: domain alignment, but left that in here to avoid conflating too many different ideas. _______________________________________________ dmarc mailing list dmarc@ietf.org https://www.ietf.org/mailman/listinfo/dmarc
