This paper presents the vision of aggregating, harmonizing, and publishing letter catalog metadata (information e.g. of senders, receivers and datings of letters) from cultural heritage (CH) institutions in Finland as a single reconciled Linked Open Data (LOD) service and a semantic portal providing data analytical tools for researchers. The research is conducted as part of the consortium research project Constellations of Correspondence (CoCo). The target of the project is to study - for the first time - scattered, heterogeneous epistolary metadata regarding the period of the Grand Duchy of Finland (1809-1917) as one, integrated dataset and make it interoperable and available. This will enable scholars to ask ambitious research questions in the field of computer science and to conduct empirical, bottom-up case studies e.g. on epistolary culture, communicative networks, and heritagization processes. This paper discusses one of the first datasets acquired by the project, the letter collection of the Board of the Finnish Art Society (1846-1901), provided by the Finnish National Gallery, which contains details of c. 1150 letters sent or received by c. 400 actors.