In your letter dated 25 Oct 2015 20:24:55 -0000 you wrote:
No idea how flexible mailman is, but how hard would it be to write some
code that ...
Instead of guessing, five seconds of googlage found this informative page:
http://wiki.list.org/DEV/DMARC
I guess this is a complex way of saying, no mailman doesn't do that?
Re your suggestion, how many subscribers to IETF lists currently use
gmail? What would happen if they were all summarily ejected?
My proposal was not to eject them but to mark them as second class citizens.
People who use unresponsive big e-mail providers off load a lot of problems
to the community.
Using a constant from should be a good incentive to look for alternatives
but does not provent people from contributing.