In a method of sorting mailpieces in a plurality of sorting passes in a sorting machine having accumulation sorting outlets, use is made of a technique for identifying the mailpieces by image signatures derived from the images of the mailpieces. The mailpieces are transferred in trays between two sorting passes. A match between a current fingerprint in the second sorting pass and fingerprints generated in the first sorting pass is searched for in an exploration memory space containing a limited number of fingerprints. The size of this exploration space is optimized by associating the signatures and the trays with designation data indicative of sorting outlets, and with time data delivered by a clock.