1. A method for sorting unaddressed mail items stored in a number of batches, the method comprising: providing a number of the batches, each of the batches being defined by respective identical unaddressed mail items; registering each batch by recording at least one pictorial reference feature of at least one of the mail items belonging to the respective batch, linking the pictorial reference feature to a sorting plan, detecting the pictorial reference feature on the unaddressed mail items during a subsequent sorting of all the unaddressed mail items of all the batches; and distributing the unaddressed mail items in accordance with the sorting plan linked to the detected pictorial reference features.