Maybe ask yourself why some users end up blocking you altogether. Surely you didn't start sending them newsletters or the like without being completely certain that they wanted to receive them, and you provide a simple, prominent and reliable way to unsubscribe if/when they change their mind, right?
There's a block-by-default setup for new email servers. You have to go through the reputation-building process which is not at all clear nor is it always guaranteed to work.
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.
