In the eighteenth century, all European colonial empires undertook the task of institutionalising their postal systems. Within the framework of the Bourbon reforms, the Spanish monarchy embarked upon reforming the postal system within the Spanish America with the aim of making transatlantic communications more reliable and regular. These plans, however, were hampered by an ongoing power struggle between all agents with a stake in the circulation of information. This is clearly reflected in the postal office in Cartagena de Indias, which was a key node for the Crown and a point of confluence for the strategies and interests of different local and global powers; the office, therefore, represented the polyhedric reality of postal communication. This paper shows that the institution had its own agency by constituting one of the main power tools, which is a reflection of the close relationship that exists between empire and communication. GECEM Project (ERC-Starting Grant), ref. 679371, under the European Union's Horizon 2020 Research and Innovation Programme, www.gecem.eu. GECEM Project (ERC-Starting Grant), ref. 679371, Horizon 2020, project hosted at UPO