Segmentation is a cornerstone of effective email marketing. By dividing the email list into smaller, more targeted groups, marketers can send more relevant content to each segment. This can be based on various factors such as demographics, purchase history, and engagement levels. Advanced segmentation strategies involve the use of behavioral triggers to send timely and contextually relevant emails. For instance, sending a follow-up email to a customer who abandoned their cart or a re-engagement email to subscribers who haven't interacted in a while.