A postal sorting machine comprises a conveyor system having a conveyor adapted to move mailpieces along a certain conveyor path along sorting outlets of the sorting machine. The sorting machine includes at least one pass sensor to detect the mailpieces in motion on the conveyor going past at a certain point of the conveyor path and to respond to a detection of the mailpiece by delivering a pass detection signal to a monitoring and control unit which responds to the detection signal by delivering a control signal for an electromechanical actuator of the conveyor. The pass sensor is a virtual sensor. A movement tracking system generates digital images of the mailpieces. An emulator generates 3D-modeled mailpieces and detects interactions between the 3D-modeled mailpieces a 3D model of the conveyor to generate the pass detection signal.