> I don’t believe Apple can dictate what ProtonMail is sending to its user via email.
They already supposedly went after apps that linked to a privacy policy on their main website because the main website itself had premium options for sale. If you can't link to legal policy etc. because it might be a level or two of indirection from offering a premium service for sale through the site you have to do something like a special site just for Apple users. I can totally see them going after email and arguing Proton mail could hide those notification emails from iOS users if they contain links to premium.
They already supposedly went after apps that linked to a privacy policy on their main website because the main website itself had premium options for sale. If you can't link to legal policy etc. because it might be a level or two of indirection from offering a premium service for sale through the site you have to do something like a special site just for Apple users. I can totally see them going after email and arguing Proton mail could hide those notification emails from iOS users if they contain links to premium.