    # File lib/vmail/imap_client.rb, line 601
        def append_to_file(uid_set, file)
          uid_set = uid_set.split(',').map(&:to_i)
          log "append to file uid set #{uid_set.inspect} to file: #{file}"
          uid_set.each do |uid|
            message = show_message(uid)
            File.open(file, 'a') {|f| f.puts(divider('=') + "\n" + message + "\n\n")}
            subject = (message[/^subject:(.*)/,1] || '').strip
            log "appended message '#{subject}'"
          end
          "printed #{uid_set.size} message#{uid_set.size == 1 ? '' : 's'} to #{file.strip}"
        end