As the volume of orders in online retail continues to grow, so does the sector's CO\textsubscript{2} emissions. At the same time, the reduction of the carbon footprint of economic activities has become a major societal concern. In this work, we study an order-assignment problem whose objective is to minimize the carbon footprint of deliveries. In this presentation, we will present how to model this problem as a Multi-item Fixed Charge Transportation problem and present several heuristic and mathheuristics for this problem.