I see, you are asking for the email address, so that people can unlock their account in case they delete their oauth token provider (i.e. their tw/fb account),

I see, you are asking for the email address, so that people can unlock their account in case they delete their oauth token provider (i.e. their tw/fb account), did I understand that correctly? But do you have to do this whenever a completely new user tries to access the website? Is setting up an alternative access method not a very different concern?