whats your definition of anonymity ?
proton mail is NOT anonymous..
in fact non of these 'secure' email services are anonymous or secure.
once you send mail from protonmail to another provider that communication is done in the clear.
open for intercept(without the need for decryption) by anyone tapped into the wire.
trust all peering points are tapped.
thats why its preferred to only communicate with addresses using the same email provider.
as those communications are encrypted on the fly.
note.. proton mail holds your PGP keys, so when forced they can turn over your private key and passphrase to decrypt
your encrypted mail.. this is what happened with RAW deal. the popular mail provider of the time was forced to turn over the PGP private keys.
bottom line.. if you're truly concerned about security, then use your own PGP keys(and host those keys locally), and require all others to provide their
public KEY. use those keys to encrypt/decrypt your communications.
anything less, and your pissing on yourself while convincing yourself its raining.