How can we as ESPs respond to them appropriately with removal of these people who don't want our emails anymore, if we don't know who the user is?
If there are any GMAIL service team members here, I would LOVE to know why a feedback loop was never implemented like the other providers.
Yes, it "works" for most people, but it also has the effect of entrenching the incumbent large email providers and preventing more independent providers from cropping up.
The current method is very lazy and collectively punishes a lot of innocent email providers for the crimes of the abusers.
It destroys competition.