How does it recognize users who already signed up?

Hello. That’s my concern. If the contents require subscription but the users will be returning several times because they need the contents, how does the plugin recognize when a user is already subscribed? Does it use a cookie? And in case the user is on another computer, it will ask him to signup again. What happens then? Can the user add his same email address and it will be then identified as already subscribed? or will the plugin refuse to grant the access due to the duplicate email address?

Thanks in advance. Best regards