I can't figure what is the Medium process when they are being contacted to regain access to an account. In a near future, we could have a "Argh I lost my email

I can't figure what is the Medium process when they are being contacted to regain access to an account. In a near future, we could have a "Argh I lost my email address" link replacing the now very common "I lost my password". Nevertheless, I have no clue what would be a standard process to recover a lost account because of a lost email address, maybe a SMS based process and personal questions like "what was your first pet name?"