Segmenting an email list means dividing subscribers into smaller groups based on interest, behavior, or signup source. For example people who joined a list after downloading a blogging guide may prefer content about writing and website growth. Another group might join because of interest in online shops or product reviews. Sending the same promotion to everyone can reduce results because not all subscribers want the same product. Segmentation allows marketers to send more relevant affiliate offers to each group. How detailed should list segmentation be for affiliate campaigns today?