I like the proof-of-work angle. Have you thought about how you'll handle legitimate first-time emails like account verification or password resets that can't complete the challenge?
these captcha farms offering solver apis can probably bypass this too, is that something on your mind? feels like in the end a paywall is the only thing left that survives agents. how do you see this playing out for the product?
Yeah I feel right now captchas can do a decent job of providing some friction, also captcha providers work on upping their game. the pay-to-deliver is what I see as the ultimate show that this message should be relevant.