As email marketers, we are regularly exhorted to make our communications more relevant. Avoid spray-and-pray, we're told, and watch response rates rise. However, most companies don't know how to send unique, personalized offers to each customer, even though today it is much easier than they suspect. Instead, most companies fall back to a divide-and-conquer strategy commonly called market segmentation. It has many benefits, but also many shortcomings.