True, but also being a bit more random where it's not trivial to filter the bot on the spammers side would make it just a little bit harder to ignore.

That's true. Unfortunately, it's not trivial to add more domains, as you'd need to own them all (to add DNS records for sending and receiving). I wanted to accept donations at some point, in the form of pointed DNS records, but realized that I couldn't do that without owning the domain, as if the domain lapsed or was transferred, Spamnesty wouldn't know and it would keep sending email from that domain, to no avail.

You could request people to home sub-domains or even register full domains for you and populate MX records etc. You simply have to test the domain records before sending. You could periodically generate a TXT record, say annually, that should be updated.

I already support several projects like this.

Out of curiosity, have you ever tried to track any stats about how often it reaches a spammer, whether it's interacting with the same spammer multiple times, etc?

While I think the donating of DNS records is an interesting idea, I personally wouldn't want to risk giving permission to an outside party for the domains I use, and I don't think it would be worthwhile to try and correctly maintain a domain just as a donation.

I don't have any stats, no. I assume most spammers are using random domains, so they wouldn't be very accurate anyway.

You could check if the MX records still point at your service, or, better yet, send a test e-mail to that domain every so often and see if it reaches your service.

Indeed, but it's added complexity and I'm not sure how many people would bother setting the DNS records I asked for. I might try it at some point, though.

This is HN, I’m sure there’s plenty of us who have spare unused domains that would do it.

I have one domain at hand that I don't use for mail at all, so people counter >= 1. I could set any MX/SPF records you want as long as I don't have to change them every two months or so... ;-)