> What is a proper gentle nudge to say "hey, your unsubscribe system is broken, please fix it"?
Report it to their email service provider via the abuse@ alias[1]. Tell the ESP what the problem is and ask them to contact their customer and clue them in. Reputable ESPs do this regularly.
Is there any information to back that up? I think it's more likely that ESPs would gladly ignore a few people in favor of their paying customers, especially since in these cases they can write those people off as "cranky privacy crackpots" who don't contribute to the consumer culture they thrive in.
I’ve done it and had well-known ESPs write personal responses (not templates) saying they’ve contacted the customer about the problem. They could be outright lying, but that probably wouldn’t scale well beyond a small support group.
I believe the incentives are more aligned than you might think. An ESP isn’t risking revenue by telling a customer that something’s not working and making them fix it. All parties know that ignoring it manifests in poor deliverability, often quickly (thanks, Gmail “Spam” button!). In my experience, your skepticism is justified about ESPs permanently shutting off a customer, but they’re comfortable doing anything short of that.