Architect a real-time Email Engine
Last updated: January 12, 2026
Quick Overview
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Salesforce
System Design
Software Engineer
Salesforce
January 12, 2026Software Engineer
Onsite
System Design
Hard
275
5
2,384 solved
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Salesforce asks this during the Onsite 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
- 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
Caching strategies (local, distributed, CDN)
API design and rate limiting
Database selection and data modeling
Requirements gathering and capacity estimation
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 would you migrate from a monolithic to a microservices architecture?
- 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
- Real-time Email Processing: The system must process incoming and outgoing emails in real-time, providing instant feedback to users regarding email status.
- **Integ...
Capacity Estimation
To estimate capacity, we need to consider:
- Daily Email Volume: Assume Salesforce has 1 million active users, each sending an average of 10 emails per day. This results in 10 million emails per d...
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