That's a great idea. I've run my own mail servers since 1999. I'd happily join a union of independent mail operators with the purpose of lobbying Google, Microsoft, and Yahoo to treat us as first-class citizens.

Start a mailing list? Or is there an existing one for this topic?

I think you should have a web page where you list your issues, show how you've done all the normal things to be considered a well-behaved mail domain. And then perhaps report your experiences with iinteracting with gmail support on the matter.

Even if it isn't deliberate, even if gmail give a fuck, as can be seen from the first (and so far only) response from anyone at Google, they're so far in the Google "We're better than everyone else and always get it right because we're geniuses" RDF that it literally doesn't matter. They can't believe that they're the problem.

Or even better: so that people stop using Gmail.