1. A postal sorting method in which mailpieces are subjected to at least two sorting passes in a machine so as to be sequenced in sorting outlets of the machine, and user processing information is available in the machine during a first sorting pass in relation to at least a certain mailpiece, said postal sorting method comprising, in a memory of a data processing unit associating said user processing information with a graphical signature of the mailpiece that is representative of an image of the mailpiece, and recovering, during the second machine sorting pass of said certain mailpiece, said user processing information that is associated with said certain mailpiece on the basis of matching of graphical signatures using a resemblance criterion.