Developer should just ask for user's email after new sign up using third party provider. Even Facebook does not require email for user to sign up. They should s

Developer should just ask for user's email after new sign up using third party provider. Even Facebook does not require email for user to sign up. They should separate the email used for the account & the email used for third party sign in. Because 1 user can have multiple third party sign in, all with different email. I think they did not need to care about customer who did not check the reply email from support, because customer can also have multiple email and did not use their primary email to sign up to your service.