Set an iCloud recovery passcode. It removes the ability to recover your iCloud account by verifying that you’re the owner but it also removes the ability of Apple to be compelled to access it.
Op: read about pgp/gpg. Do it now. When you don’t understand something ask questions about it instead of giving up.
Email was never intended to be private. It was never designed with privacy in mind and your use of a client employing an encrypted connection to your mail server does not solve the problem because tens of thousands of mail servers use unencrypted connections.
No one needs your iCloud to read your email, they can just look at the plaintext mail coming to and from the server.