In a postage meter system (FIG. 2), a user enters information,indicative of a batch of mail pieces to be franked (30). The mail pieces are franked(31), and when the batch is completed, data relating to the batch are made the subject of a cryptographic engine(33). The data digitally signed, or a message authentication code (MAC) is derived, all in a postal security device (PSD)(32). The data are communicated(34), preferably by means of public-key cryptography(35). These data are then made available to the postal authority in a secure way.(36)