Email segmentation enhances deliverability, revenue, and engagement by enabling marketers to target specific audience segments with highly relevant content. This personalized approach leads to increased engagement rates, higher click-through rates, improved sender reputation, reduced bounce and complaint rates, better inbox placement, and ultimately, improved ROI and customer lifetime value. Experts and documentation highlight the importance of segmenting based on engagement, demographics, purchase history, and other factors to optimize email performance and maintain good list hygiene. Addressing disengaged users through re-engagement campaigns or removal is crucial.