Design a large-scale Email Platform
Last updated: January 26, 2026
Quick Overview
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Morgan Stanley
System Design
Software Engineer
Morgan Stanley
January 26, 2026Software Engineer
Technical Screen
System Design
Hard
40
6
1,277 solved
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ML system design at Morgan Stanley goes beyond model selection. This Technical Screen question evaluates your ability to design end-to-end ML pipelines, from data collection to model serving, while considering production constraints like latency and reliability.
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
Monitoring and model degradation detection
ML objective formulation and metric selection
Training pipeline and infrastructure
A/B testing and experimentation
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 ensure fairness and reduce bias in the model?
- What would you do if model performance degrades over time?
- How would you debug a model that works well offline but poorly online?
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Requirements
Functional Requirements:
- User Authentication: Support for secure user authentication via SSO and 2FA.
- Real-Time Email Processing: Ability to send and receive emails in real-time with m...
Capacity Estimation
To estimate capacity:
- Daily Email Volume: Assume 10 million emails per day.
- Average Email Size: Assuming an average size of 75 KB including metadata and attachments, total data = 10,000,00...
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