Design a Email Service
Last updated: December 23, 2025
Quick Overview
Design a scalable email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Redfin
December 23, 202590
3
1,508 solved
Design a scalable 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 Redfin. 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. Redfin values engineers who can think about scalability from day one.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
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 handle a region-wide outage?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements
- Send Email: Ability to send transactional and marketing emails to users.
- Track Email Status: Provide feedback on email delivery status (sent, delivered, opene...
Capacity Estimation
To estimate capacity, we look at the following assumptions:
- Daily Active Users (DAU): Assume 10 million users.
- Emails Sent Per User: Assume an average of 0.5 emails sent per user per day. ...
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