Have you ever thought about how you can increase the open and click-through rates of your newsletter? How can you make your newsletters more interesting for your reader? There are all kinds of options to do that. One of these is segmentation based on interests.
Retention means holding on. And that's exactly what you want. You have spent money to bring in a new customer and they have ordered something in your webshop. Well done! But how do you retain that customer?