# File lib/rmail/mailbox/mboxreader.rb, line 69
      def read_chunk(size)
        chunk = read_chunk_low(size)
        if chunk
          if chunk.length > @sep.length
            @tail = chunk[-@sep.length .. -1]
          else
            @tail ||= ''
            @tail << chunk
          end
        elsif @tail
          if @tail[-@sep.length .. -1] != @sep
            chunk = @sep
          end
          @tail = nil
        end
        chunk
      end