Registering with authentic email adress

Hi all just wondering and iv'e searched a bit but couldn't find an answer. What i want to do is have new members who want to register for my forum to use thier authentic email address...in other words stop new registrations that have a Yahoo, gmail address etc..i know somewhere i can ban certain email addresses but i'm scared of accidentley banning a member if he or she already has used yahoo etc to join..the reason being we have a little pest that keeps using different ip addresses that are mainly yahoo or gmail.
Sorry if it's a stupid question.