Open-Time Ad Serving

Open-time ad serving (also called open-time decisioning or render-time serving) is a method of newsletter ad delivery where the ad auction runs in real time when a subscriber opens the email, not when the email is sent. The publisher embeds a dynamic image URL in their email template. When the subscriber opens the email, their email client fetches that URL — and the ad server runs the waterfall, selects the winning ad, and returns the creative as a 302 redirect to the image URL, all in under 5ms. Advantages over send-time serving include: impressions count only for genuine opens (not all recipients), budget pacing and frequency caps apply at the moment of delivery, advertisers pay only for real exposure, and campaigns can be updated after send. MailAdx's entire ad server is built on open-time decisioning.