Design a large-scale Email Platform
Last updated: February 28, 2026
Quick Overview
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
OpenAI
February 28, 20265
5
514 solved
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
OpenAI asks this during the System Design Round to assess your understanding of the full ML lifecycle. They want to see how you translate a business problem into an ML objective, design the feature pipeline, and plan for model monitoring and retraining.
What the Interviewer Expects
- Design the full ML lifecycle from data collection to model monitoring
- Address cold start, exploration/exploitation, and model freshness
- Discuss multi-objective optimization and ranking systems
- Plan for model debugging, fairness, and bias mitigation
- Design the feature store and training pipeline for scale
- Address model versioning, canary deployments, and rollback strategies
- Discuss the data flywheel and long-term system evolution
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle the cold start problem?
- What is your model retraining strategy?
- How would you handle a 10x increase in prediction requests?
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Requirements
Functional Requirements:
- User Registration and Authentication: Support for multi-tenant user registration, login, and secure password management.
- Email Sending and Receiving: Ability...
Capacity Estimation
Assuming OpenAI’s email platform aims to support 10 million active users:
- Daily Active Users (DAU): 2 million (20% of total users)
- Emails Sent/Received: Average 20 emails per user per day ...
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