It works sometimes. Usually, it requires phone number or email verification. This is important for protonmail to maintain a revenue stream as they don't allow multiple free accounts for the same person.
Note that even in those cases when additional verification is requested, the email addresses are not tied to your account - we only save a cryptographic hash of your email. Due to the hash functions being one-way, we cannot derive it back from the hash: https://proton.me/support/human-verification