Design Email Infrastructure for mobile apps
Last updated: December 26, 2025
Quick Overview
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Rippling
System Design
Software Engineer
Rippling
December 26, 2025Software Engineer
System Design Round
System Design
Hard
308
5
3,785 solved
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Rippling 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
Data collection and labeling strategy
Online vs offline evaluation
ML objective formulation and metric selection
A/B testing and experimentation
Model serving and latency optimization
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
- What is your model retraining strategy?
- How would you handle the cold start problem?
- How would you handle a 10x increase in prediction requests?
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Requirements
- Functional Requirements:
- Handle millions of email requests per day across multiple tenants.
- Support for sending, receiving, and storing emails securely.
- Provide features for email fi...
Capacity Estimation
- Back-of-Envelope Calculations:
- Assuming an average of 1 million users with each user sending/receiving 10 emails per day:
- Total emails per day = 1,000,000 users * 10 emails = **10 mill...
- Assuming an average of 1 million users with each user sending/receiving 10 emails per day:
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