We had a good idea early on for email spam, but we didn’t use it. There was a proposal for basically proof of work, sort of like what’s used in cryptocurrency, as a requirement to accept an email. While the threshold to defeat a lot of spam was low enough to not bother the average individual sending mail, businesses hated it because it would make it more expensive to bulk mail their users. Every time I see the thousands of bullshit emails in my inbox, I’m reminded that we endure spam to protect that.