Design a large-scale Email Platform
Last updated: November 18, 2025
Quick Overview
Design a scalable email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Databricks
System Design
Software Engineer
Databricks
November 18, 2025Software Engineer
Onsite
System Design
Medium
24
15
1,213 solved
Design a scalable email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This ML system design question from Databricks's Onsite tests your ability to think about ML systems at scale. The interviewer expects discussion of data quality, feature stores, model serving infrastructure, and A/B testing strategy.
What the Interviewer Expects
- Define clear ML objectives with appropriate loss functions and metrics
- Design a comprehensive feature engineering pipeline
- Discuss model selection with trade-offs (complexity vs interpretability vs latency)
- Plan online and offline evaluation strategies including A/B testing
- Address serving infrastructure: batch vs real-time, latency requirements
- Consider data quality, labeling strategy, and feedback loops
Key Topics to Cover
Online vs offline evaluation
Model serving and latency optimization
Feature engineering and feature stores
ML objective formulation and metric selection
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 would you do if model performance degrades over time?
- How would you debug a model that works well offline but poorly online?
- How would you ensure fairness and reduce bias in the model?
- What is your model retraining strategy?
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Solve on CodemiaSample Answer
Requirements
- Functional Requirements:
- User registration and authentication.
- Sending and receiving emails with attachments.
- Real-time notifications for new emails.
- Spam detection a...
Capacity Estimation
- User Base Estimation: Assume 1 million active users, with an average of 10 emails sent and received per user daily.
- Total emails processed = 1,000,000 users * 10 emails = 10 million emails...
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