Email was never designed to be secure. It's one of the most non-secure ways of communication possible. It heavily relies on trust, for example, nothing about email prevents you from forging who it is from, you can send an email from epstein@fbi.gov and it will arrive in a person's mailbox just like that. Email also has no built-in encryption. The security of email thus has to be enforced by centralized parties, establishing their encryption standards and networks of trust. It's just a problem with email itself. People should just abandon email for secure communication. If you really need to send something securely then send it over a Matrix server or something that guarantees end-to-end encryption and can be hosted by anyone.