One
Even better than that :Something that's worthwhile knowing for Gmail users: Gmail servers ignore any dots in the email address before the "@gmail.com", so it's possible to use a single email address multiple times
e.g.
bantzking69@gmail.com
bantz.king69@gmail.com
bantz.king.69@gmail.com
could be used for 3 different registrations on a website, or for tracking spam, or whatever, but will all end up in the same inbox.