This starts getting more complicated, but the mailing list could try
intentionally sending a message which fails DMARC (e.g., with a
claimed from address of example(_at_)yahoo(_dot_)com) to the mailing list
subscriber and see if it gets bounced, and use that to set the default
for that setting automatically?
Without exception, every suggestion made in this discussion has already
been brought up and addressed on the Mailman developers' list, or the
DMARC discussion list at dmarc.org. Perhaps people who find this topic to
be of interest could learn more faster and save everyone else's time by
reading the archives.
Among the reasons this particular approach won't work is that at some mail
providers, notably Gmail, the DMARC treatment varies both by sender and by
recipient. Sometimes they reject, sometimes they accept and deliver,
sometimes they accept and file as spam. Whatever they do to a test
message may or may not be what they do to real messages. Furthermore,
providers change their DMARC mail handling every day (which as, we may
recall, is why we have this problem in the first place.) If an operator
ignores DMARC failures today, they may do something else next week or next
year.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly