email_address_validator.rb

# From http://my.rails-royce.org/2010/07/21/email-validation-in-ruby-on-rails-without-regexp/

require 'mail'
class EmailAddressValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    begin
      m = Mail::Address.new(value)
      # We must check that value contains a domain and that value is an email address
      r = m.domain && m.address == value
      t = m.__send__(:tree)
      # We need to dig into treetop
      # A valid domain must have dot_atom_text elements size > 1
      # user@localhost is excluded
      # treetop must respond to domain
      # We exclude valid email values like <[email protected]>
      # Hence we use m.__send__(tree).domain
      r &&= (t.domain.dot_atom_text.elements.size > 1)
    rescue Exception => e
      r = false
    end
    record.errors.add(attribute, options[:message] || :invalid) unless r
  end
end