Abstract: This invention relates to a system for certifying the accuracy of postage payments based on the weights of mail pieces. The expected weight of each mail piece is determined and a mail processing unit receives data relative to the contents to be inserted into an envelope that together form the mail pieces. A high speed weighing scale is located downstream from the mail processing unit to receive the mail pieces after the mail processing unit has inserted selected materials into envelopes. A comparison is made between the expected weight of each mail piece and its measured weight. If the measured weight of a mail piece is found different than the actual weight beyond certain tolerances, it could be rejected. If a large number of mail pieces exhibit a divergence between the estimated weight and the actual weight, the mail processing unit will be disabled and an examination made to determine what caused the discrepancies in the weights.