The strong growth of e-commerce in recent years has triggered a significant increase in last mile deliveries. This increase, linked to the search for a higher level of service, has had a negative impact on the three pillars of sustainability and the need to manage last mile delivery routes in a sustainable way has arisen. However, in the current literature, most of the mathematical models aimed at route management focus on reducing the impact on the economic and environmental pillars, leaving aside the integration of the three pillars of sustainability (economic, environmental and social). In light of this situation, the aim of this research is to create a linear programming model to reduce the impact of last-mile deliveries on the three pillars of sustainability. In this way, the environmental pillar (considering CO2 emissions), the economic pillar (from the perspective of costs assumed by the company) and the social pillar (from the perspective of labour costs and working conditions through workload) are addressed. To assess the functionality of the model, it is applied to a case study and a reduction in the last-mile impact on the three pillars of sustainability is achieved. This application shows a saving of 51% of the total cost associated with the routes.