We present quantitative evidence for substantial economies of scope between letters and parcels in rural areas. The presence of economies of scope indicates that it is cost-efficient to distribute letters and parcels with the same carrier rather than having two independent delivery organizations for them separately. In the context of USO net costs calculations and operational business decisions with shrinking letter volumes and growing parcel volumes, it is important to accurately account for such economies of scope. More explicitly, considering economies of scope will likely decrease estimated USO net costs and, depending on volume conditions, USO constraints and regional characteristics, render the joint delivery of letters and parcels more attractive.