Let's clarify the purpose of DMARC and the problem of MLM edits: Modifying in-transit messages is a threat vector for both sender and recipient. The ability to constructively modify a message is also the ability to maliciously modify a message. And the ability to maliciously modify a message is also the ability to create a new message which looks like a forwarded message. In this respect, a content-editing MLM is indistinguishable from a content-fabricating spammer.
Senders do not want to be misrepresented, and do not want their good reputation to be exploited by those with a negative reputation. Recipients do not want to be misled. Consequently, sender and recipient agree to enforce DMARC policy, to prevent this from happening. If a message is altered in transit, or forged in its entirety, the message will be rejected. There are very few ways to fix this: - MLM must gain the trust of the sender and recipient, so that it can be distinguished by a spammer. - Sender and recipient must be duped into accepting content that they do not want. RFC 7960 is worded to suggest that DMARC is to blame for the problem. The real problem is that MLMs have made their operating practices dependent on weak security. Santa Claus could run into the same problem: At least in the USA, he comes down chimneys, because they are unsecured and his intentions are only good. If criminals figure out how to enter and exit through the chimney, homeowners will start placing locked grates on top of the chimney. Given the choice between "both criminals and Santa" or "neither criminals nor Santa", most homeowners would be willing to give up Santa. Of course, Santa could ask for a key, which would create a key management nightmare. Or he could ring the doorbell, show credentials, and wait to be admitted. The MLMs are like Santa. They are trying to do a good thing. But the criminals want to use the same weaknesses that the MLMs want to use. Given the choice between "both" and "neither", DMARC-enforcing domains are choosing neither. Inducing or coercing them to use "both" mode is an incorrect solution to the MLM problem. DF -----Original Message----- From: dmarc [mailto:[email protected]] On Behalf Of Dave Crocker Sent: Sunday, July 12, 2020 11:20 PM To: IETF DMARC WG Subject: [dmarc-ietf] DMARC Use of the RFC5322.Sender Header Field FYI, I've posted an initial draft for having DMARC use the Sender: field: https://datatracker.ietf.org/doc/draft-crocker-dmarc-sender/ d/ -- Dave Crocker Brandenburg InternetWorking bbiw.net _______________________________________________ dmarc mailing list [email protected] https://www.ietf.org/mailman/listinfo/dmarc _______________________________________________ dmarc mailing list [email protected] https://www.ietf.org/mailman/listinfo/dmarc
