> Nano only uses PoW as a means to discourage spammers similar to how it's used in emails.
Email does not use any such scheme. Although people have invented a couple of things along these lines (most notably, Hashcash was an email thing a decade before it was used in Bitcoin), none is widely deployed or likely to be any time soon. Yes, there is some cryptography preventing counterfeiting emails (DKIM, ARC), but that’s just signing, not deliberately-expensive-to-compute proof of work hashing.
I'm pretty sure he refers to hashcash. And while you are right, PoW is not widely used in email, I think the quote just wants to say that it's used the same way as it's used with email if/when used with email. (So the claim does not intend to be that PoW is used with email generally.)
Email does not use any such scheme. Although people have invented a couple of things along these lines (most notably, Hashcash was an email thing a decade before it was used in Bitcoin), none is widely deployed or likely to be any time soon. Yes, there is some cryptography preventing counterfeiting emails (DKIM, ARC), but that’s just signing, not deliberately-expensive-to-compute proof of work hashing.