And I'd include that as well: if your server rejects emails because of your spam-decisions, you can't claim "we've never received that email". Either you don't use email for any legally-binding communication ever, or spam-filtering is a you-problem, not an everyone-else-problem.

It's not surprising that the strongest protections always happen on the unsubscribe links, but not on the subscribe-links. That just needs to be fined out of existence, just like "you can order with one click, but you need 50 clicks and a three-hour-conversation to cancel".