Email validator

email_validator.rb

require 'resolv'

class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless value =~ /\A([^@\s]+)@([^.\s]+)\..+\z/i and valid_mx_record?(value)
      record.errors[attribute] << (options[:message] || "is not an email")
    end
  end

  private

  def valid_mx_record?(email)
    domain = email.match(/\@(.+)/)[1]
    Resolv::DNS.open do |dns|
        @mx = dns.getresources(domain, Resolv::DNS::Resource::IN::MX)
    end
    @mx.size > 0 ? true : false
  end
end