Validate email using EmailValidator strict mode

Without strict_mode, EmailValidator allows addresses with unquoted special
characters, which can cause SMTP errors when delivery is attempted.

Why do we care? If the SMTP errors aren't enough, a user that typos an address
by mistakenly inserting a special character is unable to sign in again unless
they make the same typo.

strict_mode disallows most of these special characters, quoted or not, which
seems more appropriate than allowing them. When is the last time you saw an
address such as 'first";"last@gmail.com'.