Proton Mail
Encrypted email from Switzerland.
Free email from Big Tech is paid for with your inbox, scanned to build ad profiles and shared with third parties. A private email provider runs on a different deal. Paying with a subscription means the company has no reason to mine your mail for ads. How much the provider itself can read varies. The strongest lock your mailbox so even they cannot open it. Others encrypt less. The right pick depends on how much you need them shut out.
Email was never built to be private. The headers sit outside any end-to-end encryption, which leaves who you write to, when, and usually the subject line visible to the servers in between. Encrypting the body itself needs both people to hold keys. The open standard for that, OpenPGP, works across different providers once you have traded public keys, while some services use their own scheme instead. A good provider builds this in and keeps the rest of the leakage down.
Here are some things to look for.
Encrypted email from Switzerland.
Lightweight encrypted mail with its own encryption scheme.
Dutch nonprofit email with self-held GPG keys and Monero payment.
Norwegian email with strong jurisdiction but no encryption at rest.