A method of sorting mailpieces by using a dynamic assignment process and an overbooking mechanism whereby an overbooked sorting destination (D) is substituted for a sorting destination that is already assigned to a certain sorting outlet (S) comprises the following steps: a) identifying from among said sorting outlets (S) a sorting outlet that has a filling level (N) greater than a first threshold (s1) and the longest idle time, and assigning the overbooked sorting destination to that sorting outlet; b) if all of the sorting outlets (S) have filling levels (N) less than said first threshold (s1), identifying from among the sorting outlets the sorting outlet that has the longest idle time, assigning that sorting outlet to said overbooked sorting destination, and indicating that said other sorting destination is a sorting destination to be amalgamated.