A sorting machine for sorting mailpieces including both letters and flats comprises: a first sorting system (20) adapted for flats and including a first mailpiece conveyor suitable for directing the flats towards sorting outlets of the type having racks (26) into which the flats fall by gravity; and a second sorting system (1) adapted for letters and including a second mailpiece conveyor suitable for directing the letters towards sorting outlets of the type having stackers (7) in which the letters are stacked on edge one behind another. The two sorting systems have the same number of sorting outlets, the two systems being superposed so that the sorting outlets of the first sorting system are superposed on respective ones of the sorting outlets of the second sorting system. Each sorting outlet of the first system may be equipped with at least two racks towards each of which a flat can be directed selectively by the first conveyor.