Re: haveibeenpwned
Not my particular one, no. I wouldn't even claim to understand it any more!
It's a complex regexp built up over years, but to give you an example:
If I wanted to give, say, Microsoft an address.... I could use microsoftnn@domain.
And nn would be a factor of the word "microsoft". For instance, length. Or how many vowels (easily countable in your head). Or some similar metric / formula.
Then if I'm asked on the fly for an email, I can craft one. If someone makes one up and doesn't know the rule, it won't generate a valid email. Email that doesn't meet the regexp (in the "virtual" alias file in Postfix, for example) will just bounce as not being valid. New emails don't require me to explicitly set them up, so long as they match the rule (and because it's a virtual alias, all valid ones at my domain are just forwarded to my real email account on one line). And when I receive them at the endpoint, I know if it came from my mail server it must have matched those rules.
I don't even do things THAT simply... the address wouldn't be microsoft, for instance, but something I know that is related to Microsoft... i.e. I might use "redmondnn@" for example. Then if I get an email purporting to be from Microsoft and it's addressed directly to my final email account... it's a fake. If it's addressed to anything other than redmondnn@, then it's a fake. And if it's addressed to redmondnn@ then I know that that is the precise email that I gave Microsoft and Microsoft alone (so either they have released that email somehow, or I've been compromised).
And yet when I speak to companies or sign up on their website on a foreign device, all I need to do is make up an email, work out the "score" that goes on the end in my head, and provide it to them and they likely would never query it at all because it just looks like an ordinary email address ("johnsmith43@" etc. are common).
One regexp, and I'd have to sit and spend a week deciphering it admittedly because it's more complex than the above!, and all my "phishing identification" and catch-all spam goes away.