1. A method for detecting overlapped mailpieces when singulating batches of flat mail pieces as the pieces are conveyed on their narrow sides, whereby the sorted mail pieces are moved successively standing on their narrow sides in a longitudinal direction along a bed or belt path, whereas positioned below the transport path is an electronic line camera with its optical longitudinal axis perpendicular to the transport direction of the mail pieces that scans the bottom edges of the mail pieces through an aperture in the base plate whereas two sources of light are positioned laterally from the mailpiece bottom edges in order to diagonally illuminate the bottom edges of the mail pieces from below as the mail pieces pass over the aperture of the base plate so that the bottom edges of the scanned mailpieces are emphasized by shadowing, furthermore the output of the electronic line camera is fed to an evaluation means which calculates the statistical characteristics of the line by line scanned mailpiece bottom edge image and compares them with those of off-line predetermined sets of characteristics derived from typical samples of bottom edge images representing different physical class models of known single feed as well as double feed bottom edge image constellations, in order to determine as the decision result the class model with the highest probability of representing the measured characteristics.