Design a Email for Jane Street
Last updated: February 19, 2026
Quick Overview
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Jane Street
February 19, 20261
9
3,399 solved
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during Onsite at Jane Street. 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. Jane Street values engineers who can think about scalability from day one.
What the Interviewer Expects
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
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 happens if one of your database nodes goes down?
- What monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
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Requirements
- Functional Requirements:
- Users must be able to send and receive emails in real-time.
- Support for attachments (up to 25MB).
- Search functionality for emails using various filters (date...
Capacity Estimation
Assuming Jane Street has approximately 10,000 active users globally:
- Email Volume:
- Average 50 emails per user per day = 500,000 emails per day.
- Peak load during trading hours can spike ...
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