A server-to-server tracking mechanism in affiliate marketing where conversion data is sent from the brand's server directly to the affiliate network's server via an HTTP request, without relying on browser cookies. Also called a postback, S2S tracking, or server-to-server (S2S) postback. How postback URLs work: when a consumer clicks an affiliate link, the network generates a unique click ID and passes it to the brand's site as a URL parameter; the brand stores this click ID alongside the consumer's session throughout the shopping experience; when the consumer completes a purchase, the brand's server fires the postback URL (an HTTP GET or POST request to the affiliate network's server) containing the click ID, order value, order ID, and other conversion data; the network receives this server-side notification and records the conversion; no browser cookie is needed. Advantages over cookie-based tracking: resistant to browser cookie blocking (Safari ITP, Firefox ETP, browser extension blockers); resistant to cookie clearing by consumers; more reliable in cross-device scenarios; compatible with GDPR consent requirements (doesn't require browser-side cookie consent for the tracking mechanism itself); typically captures 10-30% more conversions than cookie-only implementations. Implementation requirements: postback tracking requires development work to: capture and store the click ID parameter from the affiliate link; maintain the click ID through the checkout flow; fire the postback HTTP request at conversion with the click ID and order data; most major networks (Impact, Awin, CJ, ShareASale) provide postback URL documentation, testing tools, and implementation guides. When postback is required: EU/UK programs (GDPR compliance); programs experiencing significant tracking loss in Safari/iOS environments; high-value programs where tracking accuracy directly impacts commission budget allocation.
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