Design a Email Service
Last updated: April 19, 2026
Quick Overview
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Dropbox
April 19, 202680
7
4,676 solved
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Dropbox asks this during the System Design Round to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Clearly define functional and non-functional requirements
- Propose a reasonable high-level architecture with core components
- Choose appropriate data storage solutions with basic justification
- Discuss basic scaling strategies (horizontal scaling, caching)
- Identify potential bottlenecks and suggest simple solutions
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
- What monitoring and alerting would you set up on day one?
- How would you handle a region-wide outage?
- How would you handle schema migrations with zero downtime?
- How would you handle a 10x increase in traffic overnight?
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Requirements
Functional Requirements:
- Multi-Tenant Support: The email service should allow multiple users from different organizations to have their own email domains and accounts.
- **Sending/Receivin...
Capacity Estimation
Assuming Dropbox targets around 10 million active users:
- Emails per User: Each user sends/receives an average of 20 emails per day.
- Total Emails per Day: 10 million users * 20 emails = 200...
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