The management of natural environments has become a fundamental issue for companies in recent years. A firm’s environmental commitment affects all levels of its operation. In this study, we investigated whether having an effective and constant relationship with customers over time (customer capital) makes a difference to firms with a high environmental commitment compared with less environmentally committed firms. We found support for our idea by using original survey data from 149 small and medium-sized enterprises (SMEs) in Iran (2016–2017). Furthermore, we found that customer capital enhances environmental collaboration with customers which, in turn, has a positive impact on the firm’s environmental commitments. These findings provide empirical evidence for the important role of “getting closer to customers” as a way of enhancing corporate environmental responsibility in developing countries with weak institutional environments.