# File lib/rmail/header.rb, line 404
    def to_string(mbox_from = false)
      s = ""
      if mbox_from && ! @mbox_from.nil?
        s << @mbox_from
        s << "\n" unless @mbox_from[-1] == ?\n
      end
      @fields.each { |field|
        if field.raw
          s << field.raw
        else
          s << field.name
          s << ': '
          s << field.value
        end
        s << "\n" unless s[-1] == ?\n
      }
      s
    end