1. A system for generating printed mail pieces, starting from a print file, comprising: a printer for printing postal items; a processing device for processing printed postal items into mail pieces; a control unit for controlling the printer and the processing device, comprising an input interface for inputting a rough print file for controlling a printer, which rough print file at least partly defines at least one document to be printed, a processor for processing the rough print file in accordance with processing instructions into a processed print file, an output interface connected with said printer and with said processing device for transmitting control signals to at least said printer or said processing device for controlling said printer and said processing device in accordance with, or formed by, said processed print file, and memory containing: processing code for controlling said control unit for processing said rough print file into a processed print file, which processing code comprises processing instructions; and representation code for causing said processing instructions to be represented in humanly perceptible form, said representation code being editable for changing at least said representations of said processing instructions, and said representation code being convertible into said processing code.