Efficiency in email marketing refers to the capability of delivering the right message to the right audience at the right time with minimal resources. This can be achieved through segmentation, automation, and A/B testing. Segmentation allows you to divide your audience into different groups based on criteria like demographics, behavior, or purchase history. Automation tools can help you send timely and relevant emails without manual intervention. A/B testing enables you to determine which versions of your email perform better, helping you optimize future campaigns.