Apparatus and method for a modular postage accounting system. An open system metering device of the present invention includes a general purpose computer, a digital printer and a secure metering device (SMD). The SMD performs the accounting functions of a postage meter and generates encrypted postage indicia data for transmission by the computer to the digital printer and subsequent printing on a mailpiece by the digital printer. Postage credit data can be entered into the SMD using a computerized meter resetting system just as it is in a conventional postage meter.