Segmentation splits subscribers into groups for targeted sends — by interest tag, engagement level, purchase history, or signup source. Segmented campaigns typically achieve 15–30% higher open and click rates than broadcast-to-all sends. Common segments: engaged (opened in 30 days), inactive (no opens in 90 days), paid vs free, topic interest tags. Effective segmentation is one of the highest-ROI tactics for creators with lists above 1,000.