Design a Email Service
Last updated: December 15, 2025
Quick Overview
Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
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Design a multi-tenant email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during System Design Round at LinkedIn. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. LinkedIn values engineers who can think about scalability from day one.
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
- How do you ensure data consistency across multiple services?
- How would you migrate from a monolithic to a microservices architecture?
- How would you handle schema migrations with zero downtime?
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Requirements
Functional Requirements:
- Multi-Tenant Support: The email service should handle multiple users from different organizations while ensuring data isolation.
- Email Sending and Receiving:...
Capacity Estimation
To estimate capacity, let’s assume:
- Number of Users: 100 million users.
- Average Emails per User per Day: 10 emails.
- Total Emails per Day: 100 million users * 10 emails = 1 billion em...
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