Our rediscovery of a seventeenth-century postmasters’ trunk in the Museum voor Communicatie in The Hague, containing some twenty-six hundred undelivered letters mostly sent from France, offers the opportunity to rethink what constitutes an archive and how to approach it. First, we argue that understanding the process of loss, destruction, and survival of collections is a crucial exercise for historians. Practising this “archaeology of the archive” makes us keenly aware that the questions we ask are often dictated by the genesis and structure of the archive. In addition, our team has developed new strategies to ensure responsible access to this unique collection through Early Modern Letters Online, including the material features of the preserved letters. The work of our colleague Jana Dambrogio at MIT Libraries has fundamentally changed how we approach our materials. She has revolutionised the field of paper conservation by creating the field of “letterlocking”: the process by which a substrate such as paper, parchment, or papyrus has been folded and secured shut to function as its own sending device. The Brienne Collection preserves an astounding variety of letterlocking practices, thus allowing us to think from the ground up how to describe early modern letter collections, and how best to make them accessible via cataloguing strategies, database links, image files, videos, and editorial practice.