I really want unlimited aliases for signing up to sites and tracking who is leaking my data.

I sign up with a different email address on every website. (I have a catchall at my domain, rather than using plus-addressing.)

The results are more boring than you think. Almost no one leaks my address. A couple have been hacked, but almost all of those are widely known. (I did discover one early and help Troy Hunt validate a leak.) At least one Kickstarter campaign has shared my address, as has a local business. But that seems to be the extent of it.

I still do it, because I did manage to catch those things, and because it reduces cross-site correlation. But yeah, there's less skeevy behavior than you might think.

You can do something like email+site@gmail.com and it'll be delivered to email@gmail.com with the site in the To field

I find that just about everybody is leaking my data. Either on purpose or accidentally. But at the end of the day I do want to order those online exotic vegetables and have very little choice of sites to do it in my country. At this point I don't care anymore. Maybe I should but in a sense it's too late. It's been decades of leaked information, I'm certain the advertising companies know me better than my friends. And still royally fail at selling me stuff. They likely use this info for more nefarious things.

I hate that 90% of the effort on the internet is about stealing information from users and serving invasive ads.

mailbox.org hooked up to Thunderbird allows you to do so using custom domains. You can send and receive email as any string @ your domain.