As the e-commerce sector continues to grow, customers are increasingly concerned about the impact of their online orders on working conditions and the environment. In many cases though, online retailers emphasize delivery speed over sustainability and offer delivery options that put a strain on logistics workers and the environment. To promote the choice of more sustainable but slower delivery options, we present a model concerning how message frames affect delivery choice and customer outcomes (order completion, loyalty, word of mouth). An experimental study shows that simple message frames, regarding job conditions, the environment, and customer convenience, increase the choice of more sustainable, slower delivery options and customer outcomes indirectly via delivery choice, and warm glow feelings. Delivery fees dilute the impact of environmental message frames on delivery choice though. Overall, our findings suggest that nudging customers towards sustainable delivery options is possible, yielding positive effects for customers and retailers.