def provider
      return @provider if defined? @provider
      EmailAddress::Config.providers.each do |provider, config|
        if config[:exchanger_match] && self.matches?(config[:exchanger_match])
          return @provider = provider
        end
      end
      @provider = :default
    end
def provider
      return @provider if defined? @provider
      EmailAddress::Config.providers.each do |provider, config|
        if config[:exchanger_match] && self.matches?(config[:exchanger_match])
          return @provider = provider
        end
      end
      @provider = :default
    end
Returns the provider name based on the MX-er host names, or nil if not matched