lib/mail_form/delivery.rb
def spam?
      self.class.mail_captcha.each do |field|
        next if send(field).blank?

        if defined?(Rails) && Rails.env.development?
          raise ScriptError, "The captcha field #{field} was supposed to be blank"
        else
          return true
        end
      end

      false
    end
def spam?
      self.class.mail_captcha.each do |field|
        next if send(field).blank?

        if defined?(Rails) && Rails.env.development?
          raise ScriptError, "The captcha field #{field} was supposed to be blank"
        else
          return true
        end
      end

      false
    end
In development, raises an error if the captcha field is not blank. This is
 is good to remember that the field should be hidden with CSS and shown only
 to robots.

 In test and in production, it returns true if all captcha fields are blank,
 returns false otherwise.