You register with a username and a password. The username must be alphanumeric and must fit within the local part of an email. But actually let's limit it to 32 characters (instead of 64), we'll need more space later. Let's say your register as "johndoe".

You are assigned a randomly generated unique id with all kinds of symbols and shit (because it will act as a salt). Let's say for you it's "!#$!$%^!@#$^#$^@#$^!" (which yes, I got by holding shift and mashing on the numbers).

Now let's say you want to register for twitter, and of course, you need an email for that. So you log in to my website (let's call it example.com), and go to "Create new hash address". You type "twitter". Your new email is the sha256 of your unique id + a new random id (let's say "%@*@%!#$^&%!#$!") + "twitter", so:

6e6d7f7e10c619267682de5b5867679a510de1c3f2e5df8c852cf909d16407b4@example.com

(Rather long but it's a valid email.)

You copy-paste that shit and register with it.

You can create as many addresses as you want. There is no spam filters. You can see exactly where you're receiving exactly which kind of spam from. You can know exactly what services shared your email with advertisers or spammers.

And you can filter all of that shit. Your inbox is a combined set of different addresses of your choice, or you can check each address individually.

Somebody automatically opted you in to some unholy mailing list? Some newsletter you don't care about? Any kind of bullshit at all? Maybe something you actually wanted at some point but don't care about anymore and can't figure out how to disable now? Just filter the address out of your inbox. Don't look at that shit again until you actually need to.

Now you want your buddy to send you emails. You go to "Create new friendly address". You type "friends". Your new email is johndoe.friends@example.com.