Design a distributed Email System
Last updated: February 14, 2026
Quick Overview
Design a distributed email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Elastic
February 14, 2026262
5
3,136 solved
Design a distributed email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This fundamentals question from Elastic's Onsite tests whether you can reason about software design at a deep level. The interviewer expects discussion of maintainability, testability, and operational considerations.
What the Interviewer Expects
- Apply engineering principles to a realistic design scenario
- Discuss trade-offs between different approaches with concrete examples
- Demonstrate understanding of testability, maintainability, and extensibility
- Connect theoretical concepts to production engineering practices
- Discuss how the approach scales with team and codebase size
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- How would you measure the performance of this component in production?
- How would you document this for other engineers?
- What are the security implications of this design?
- How would this design change if the team size doubled?
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Core Design Principles
For the distributed email system, several core design principles apply:
- CAP Theorem: This states that a distributed system can provide only two out of three guarantees: Consistency, Availabili...
Architecture
The architecture for the distributed email system will adopt a microservices approach:
- Microservices: Each service (e.g., SMTP service, IMAP/POP3 service, User Management, Notification Service...
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