In a postage payment system, a secure integrated circuit (IC) card is used to manage postage funds, and create encrypted postage indicia. Among other things, the system is capable of performing charge-back accounting of postage expenses and generating mail contents. In accordance with an aspect of the invention, the postage indicia are applied onto selected locations of the mail contents while they are being generated. In the preferred embodiment, each mail content is placed in a window envelope such that the postage indicium on the mail content exposes through a window of the envelope to facilitate inspection of the indicium. In accordance with another aspect of the invention, by including transactional data in addition to the traditional postal data in a postage indicium, the indicium can be used to pay bills, purchase products and services, including any courier service different than the postal service.