You delete the rest of your spam database and replace it with `fn can_send_spam(_: Email) -> bool { false }`. You delete the "can we spam you" checkbox from your checkout page and replace it with "return false".

For legitimate newsletters and similar: you delete any and all forms that allow signing up to receive emails without affirmative consent from that email address that they want to receive mail, and you offer a one-click effective-immediately "unsubscribe" to retract that consent at any time. Then, you can tell if you can send someone mail based on whether they're in your database of people who have explicitly consented to send you mail, and you don't ever send email to anyone else other than one-time consent requests and order-confirmation-style transactional mail.

The only legitimate database of emails is "these people have explicitly confirmed to us that we can email them"; any other database is radioactive waste, delete it.