Comment by notpushkin

A certain tongue-in-cheek email provider [0] uses . (a dot) for this purpose, i.e. username.anything@domain.tld. Spammers could remove the distinguishing part here too, but they can't be bothered to keep a list of all the conventions used by different providers, so I think it should work pretty well.

(Personally I use a dedicated catch-all domain now, and the username is the distinguishing part – try to remove that!)

[0]: https://cock.li/, they do have SFW domains though