The issue I’m seeing with any free plans of email providers is that they either require an identifying verification, or don’t allow the email to be used for services.
tutamail, for example, states that the free plan is not to be used to signup for services.
protonmail requires verification by email ‘to prove you are human’.
Thank you
Could be a more recent change? I tried this about 6 months ago. I got around it using a temp email, though. Admittedly I don’t use that account for much, and should probably delete it xD