Build a real-time Email Pipeline
Last updated: November 5, 2025
Quick Overview
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HubSpot
November 5, 20252
6
4,994 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 Technical Screen at HubSpot. 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. HubSpot 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 would you optimize costs as the system scales?
- What would the deployment pipeline look like for this system?
- How would you migrate from a monolithic to a microservices architecture?
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Requirements
Functional Requirements
- Real-time Email Processing: The system should process incoming email requests within seconds.
- Queue Management: Handle millions of email requests using a mess...
Capacity Estimation
Assuming HubSpot sends out 2 million emails per hour:
- Requests Per Second (QPS):
- 2,000,000 emails/hour = 2,000,000 / 3600 seconds = ~555 QPS.
- Storage Needs:
- Average email size ...
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