System designHardsd-g086

Subject PersonalizationLevel Senior–Staff~50 minCommon in Distributed systems interviewsIndustries Technology

Question

Design a personalized notification/email send-time + content-selection system for a 50M-user app that decides for each user WHICH message to send and WHEN, to maximize long-term engagement without fatiguing users into unsubscribing. It must learn per-user from sparse feedback (opens/unsubs), adapt within days, and cap message frequency.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.