1. A computer-implemented method in a server computing system for facilitating the production of shipping labels, the method comprising: causing a shipping label to be produced by a client computing system that is separate and remote from the server computing system, by, transmitting, to a Web browser executing on the client computing system, a first uniform resource identifier having a scheme name and scheme data, the scheme name identifying a shipping protocol and configured to cause the Web browser to execute a shipping label module on the client computing system, the scheme data including shipment information and post-back information, the shipping label module configured, when executed, to produce the shipping label in accordance with the shipping protocol by: initiating output of the shipping label based on the shipment information; and automatically posting information about the produced shipping label back to a computing system remote and separate from the client computing system, based at least in part on the post-back information.