Interesting project. I was recently inundated with abusive account signups, and it seemed like the "fast path" for attackers was to register an outlook.com domain, and use that to create a Github account. I guess Microsoft does no validation on these signups. It was especially painful since legit users used outlook.com and Github, so I couldn't just block them. (Fastmail is in second place here, but had no legitimate use, unfortunately.)

For emails that I don't want an ongoing obligation to read... I used to have a custom alias for mailinator (nospam.jrock.us MX <them>). At some point I guess I got rid of it, perhaps because mailinator stopped offering that service. Unsurprisingly, nobody ever looks up the MX record to implement the denylist. Worked perfectly every time.