# File rmail/header.rb, line 339
    def to_string(mbox_from = false)
      s = ""
      if mbox_from && ! @mbox_from.nil?
        s << @mbox_from
        s << "\n" unless @mbox_from[-1] == ?\n
      end
      each { |n, v|
        s << n
        s << ': '
        s << v
        s << "\n" unless v[-1] == ?\n
      }
      s
    end