A method of processing mailpieces for sorting mailpieces into sequence in a sorting machine depending on delivery points of delivery rounds, in which method the mailpieces are grouped together into batches associated with delivery rounds and are sorted as a function of various sorting plans each associated with a respective batch of mailpieces and defining a list of delivery points of delivery rounds, which method includes the following steps, assessing the batches of mailpieces before the machine sorting to detect those that will under-use the sorting capacities; aggregating the batches of mailpieces detected as under-using the capacity so as to constitute aggregated batches of mailpieces; computing an associated sorting plan resulting from the aggregating; feeding each aggregated batch of mailpieces into the postal sorting machine and controlling the sorting of the mailpieces as a function of the sorting plan computed for said aggregated batch of mailpieces.