> I wonder what the best avenue is to actually make that the default. It's almost certainly not this kind of unannounced cutoff.

En contraire, I think not delivering mail is the fastest way to adoption. People will use an old system for as long as it works. It now does not anymore.

I don't know. I think this disenfranchises a lot of independent operators, and the blow of that could at least be softened by making a highly-visible public announcement about it a few months ahead of time.

Maybe you're right that just enforcing it is the way, but I don't agree with doing that with no heads up.