Privacy-focused email doesn’t truly exist, since it’s likely 90%+ of people you email are probably using Gmail, Hotmail/Outlook, or Yahoo. Companies like Gmail/Google could still build a profile of you if they wanted to, by collecting all the threads you’re a participant in.

The best you can do is self-host your mailbox (e.g. Using Mailcow) with an encrypted file system (e.g. using LUKS), but you’d still need to use an SMTP gateway to ensure deliverability, so it’s going to be relayed through, and ultimately end up at, some third-party you have no control over. Some third-parties don’t even have TLS enabled for their email servers.

You shouldn’t think of email as a private or secure communication mechanism unless you’re encrypting your emails.