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'.