Jeff Lee doesn't just build marketing campaigns. He engineers lifecycle systems that quietly power billions of customer interactions. As the lifecycle marketing technical lead at Calm, Jeff runs a team of four, shipping 240+ distinct email campaigns a year and moving data across Databricks, Iterable, and Amplitude with precision most teams can't match. In this conversation, he makes the case for marketing engineering as a distinct discipline, sitting between data engineering, product, and marketing to solve problems no one else owns. We dig into the "Sorting Hat" automation that prioritizes message delivery at scale, why he'd never build an ESP in-house again, the downstream cost of a three-line code bug that tanked opt-ins by 60%, and why attribution, personalization, and end-to-end lifecycle orchestration depend on engineers who think like marketers and marketers who think like systems architects.Timestamps05:12 — The three-line code bug that killed 60% of email opt-ins overnight 22:03 — Inside the "Sorting Hat": How Calm prioritizes lifecycle messaging without global caps 31:47 — Why cutting your martech budget by 50% should start with list hygiene, not tools 37:14 — Jeff's dream stack and why CDPs are overrated 46:16 — Where AI breaks in lifecycle marketing 52:26 — Making "marketing engineer" a real job titleSponsorBrought to you by Hightouch, the leading composable CDP and decisioning platform trusted by brands like Domino's, Chime, and Aritzia. 90% of customers have a real use case live within their first week, delivering world-class personalization at scale. Learn more at hightouch.com/msom.Connect & SubscribeSubscribe to Making Sense of Martech wherever you get your podcasts. Follow us on TikTok, LinkedIn, and don't forget to like and subscribe on YouTube.