Abstract: The present invention deals with a microprocessor implemented method and system suitable for use in a mail sorting machine to sort the envelopes into common groups, assign each group a particular sort bin and generate a coded bin designation signal. The envelopes to be sorted are run through the machine in two passes. During the first pass, the system causes each of the envelopes to be deposited in a designated sort bin in accordance with a sort table which was programmed into the microprocessor prior to the first pass. The microprocessor also compiles a list of the zip codes of each envelope moving through the machine and maintains a count of the number of envelopes having each zip code. Once the first pass is completed, the microprocessor assembles the compiled zip codes into common groups and assigns each group a bin location. The microprocessor then assembles the bin locations into a sort table and outputs a list of loading instructions.