1. A method of sorting mailpieces in a plurality of sorting passes in a postal sorting machine provided with sorting outlets wherein delivery points recognized for said mailpieces are assigned to said sorting outlets so as to sequence the mailpieces in the sorting outlets for delivery in an order of a delivery round, said method comprising the steps of: retrieving from a database, statistical data representative of mail volumes delivered respectively for said delivery points, constructing into said machine disjoint subsets with said delivery points, each subset comprising successive delivery points grouped together in such a way that a cumulative weight of statistical data associated to the delivery points of said subset is less than a predefined threshold, and assigning said subsets of delivery points to said sorting outlets so that the delivery points of each subset are associated every time with a common sorting outlet for sequencing said mailpieces in the sorting outlets.