This project considers that e-commerce has grown in the last years and for the consumer, what would previously have been a trip to a store is now delivered to the home. However, in a quest to achieve even larger profits and market share, e-retailers compete to make lucrative offers to consumers, such as free shipping, expedited deliveries, and free returns. This has made last-mile deliveries even more demanding, both economically and in terms of environmental sustainability. To keep pace with the growing demands of e-commerce, last-mile operators have developed, tested, and implemented various last-mile strategies around the globe. While these measures have been studied in the literature, little is yet known about the comparison of the different strategies of last-mile operators against each other and which works best under different conditions. It is precisely this gap in the knowledge that this study aims to fill. The objective of this work is to develop a last-mile delivery optimization model based on Continuous Approximation (CA) techniques and cost-based sustainability assessments, capable of testing various last-mile strategies (e.g., consolidation centers, micro-hubs, electric vehicles, pickup point locations, cargo bikes, and the use of crowdsourced deliveries). With this, the researchers expect to develop an unprecedented understanding of the capabilities of different last-mile strategies under varied environments.