Amazon's terms of service prevent sellers from directly emailing customers acquired through the marketplace — but every fulfilled order represents a buyer whose preferences and purchase behavior can inform smarter marketing on other channels. The integration pattern is to sync Amazon order data into Klaviyo as a custom property on a contact record, enabling segmentation by product category purchased, order frequency, and recency without violating Amazon's messaging rules. Sellers use this to build Klaviyo audiences of repeat Amazon buyers and target them via Meta or Google ads, or to suppress Amazon buyers from Klaviyo email flows that would duplicate Amazon's own transactional messages. Setup requires a middleware tool because there is no native Klaviyo-Amazon connector; Make's Amazon module combined with Klaviyo's profile API is the most common approach.