Email validation for exotic characters

Question

It seems that the email validation in Grails just apply a simple regex. While it validates most emails, some exotic but authorized characters will make the validation fail.

The German ß character for example is used in some email addresses, but won't pass the grail validation:

package com.stuff.user.AppUser

import grails.test.mixin.Mock
import spock.lang.Specification

/**
 * Created by hschoonjans on 21/03/2016.
 */
@Mock(AppUser)
class AppUserSpec extends Specification {

    def "It doesn't validate an email with an eszett"() {
        given:
        AppUser user = new AppUser(email: "helainß@hotmail.com")

        expect:
        !user.validate(["email"])
    }
}

Using a custom regex for validation, authorizing the ß would be trivial but what if a user tries to use another exotic yet valid character in his mail address?

To avoid this problem, I would like to know what Java/Groovy/Grails universal email address validator exist. A class/regex that would validate any valid email address, smarter than the current Grails email validation.

Answer 1

I've come across this several times before in my own Grails projects and I've had pretty good success using this RegEx:

/^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$/i