A method is specified for sorting flat mail items, which allows sorting according to delivery order to be carried out swiftly and reliably. With the method a first sorting pass is carried out in a first segment with at least N storage modules of a sorting device and a second sorting pass is then carried out in a second segment with at least N storage modules of the sorting device. The overflow items, which are assigned to a storage module that has been closed because it is full, are deposited into one of the other storage modules in the first sorting pass and are included in the sorting process of the second sorting pass.