Giving large providers a taste of their own medicine might be interesting, let gmail spend 24 hours on a black hole list, make sure the removal forms have a captcha so they can’t be filled out by automation, when people complain on social media then let people know what it’s about. Social media really gets Google’s attention, it draws them out from behind their algorithms and silence when nothing else will.

Utilizing IPv6 more might help also since at some point it becomes absurd to have quintillions of addresses blocked for all eternity.

There are monopoly and racketeering angles also, since Google and Outlook are suppressing independent mailers in favor of their own paid products. Nobody will make any money except the lawyers but that’s ok as long as the situation improves.