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Design a temporary email service
SMTP Protocol and MX RecordsDistributed Message Queues/StreamsNoSQL Databases with Time-To-Live CapabiliObject Storage with Lifecycle PoliciesRate Limiting and Abuse Prevention Strateg
Design a Disposable Email Service with Auto-Expiring Addresses
Design a receive-only disposable email service, similar to "10-minute inboxes," that issues auto-expiring email addresses and displays received messages via a web UI and REST API.
Functional Requirements
- Ephemeral Address Creation: Allow users to create temporary email addresses that automatically expire after a specified duration (e.g., 10 minutes).
- Email Ingress: Receive inbound email over SMTP and make messages available for display in near real-time.
- Message Management: Provide functionality to list, read, and delete messages via both a Web UI and a REST API.
- Quotas and Rate Limits: Enforce per-inbox and per-user/IP quotas and rate limits to prevent abuse and manage resources.
Non-Functional Requirements
- High Availability: Ensure high availability for SMTP ingress and message reads. Eventual consistency is acceptable for message indexing.
- Low Latency: Display new messages with low latency, targeting a p95 of less than 2-5 seconds from SMTP acceptance to display.
- Scalability: The system must scale to handle millions of inboxes and millions of messages per day.
- Privacy and Security: Maintain strict privacy and security standards, including compliant deletion of messages upon TTL expiration.
- Cost Efficiency: Implement cost-efficient solutions, particularly concerning storage lifecycle management.
Key Areas for Discussion
Your design should provide a clear, high-level overview and specifically address the following aspects:
- Requirements and Public APIs: Define the core APIs for operations like creating an inbox, listing messages, retrieving a specific message, and deleting messages.
- Address Generation and TTL Semantics: Detail how ephemeral email addresses are generated and how their time-to-live (TTL) is managed.
- SMTP Ingress: Describe the setup for MX records, the behavior of the inbound Mail Transfer Agent (MTA), and the email acceptance policy.
- Spam and Abuse Controls: Outline strategies to mitigate spam and prevent service abuse.
- Storage Schema and Indexing: Propose a storage schema for inboxes and messages, including how per-message TTL is handled and the indexing strategy for efficient retrieval.
- Message Retrieval: Explain the mechanism for retrieving messages via the Web UI and REST API, including the authentication model or use of capability tokens.
- Rate Limiting and Quota Enforcement: Detail how rate limits and quotas are implemented and enforced.
- Privacy and Security: Discuss measures for inbox isolation, link-safety within messages, and handling of attachments.
- Compliance and Deletion Guarantees: Describe how compliance requirements are met and how deletion upon TTL expiration is guaranteed.
- Background Cleanup Processes: Outline the processes responsible for cleaning up expired inboxes and messages.
- Observability: Detail the approach to metrics, logs, tracing, and alerts for monitoring the service.
- Capacity Planning and Cost Controls: Discuss strategies for capacity planning and mechanisms for controlling operational costs.
Architectural Considerations
Consider the following architectural elements in your design:
- High-level Architecture: A typical flow might involve an MTA feeding into a queue/stream, processed by a message processor, stored in a durable store, potentially cached, and then exposed via an API/UI.
- Data Model: Define the entities for inboxes, messages, and attachments, along with any necessary indexing entities.
- Consistency vs. Availability: Discuss the trade-offs between consistency and availability, particularly for SMTP acceptance, message availability, and deletion.
- Scaling Strategies: Detail how the system will scale to handle millions of inboxes and messages daily.
- Cost Control Mechanisms: Elaborate on strategies like storage lifecycle management, attachment size limits, and rate limiting to manage costs.
AI interview prep
Core dilemma
Balancing the extreme write throughput and low-latency retrieval of transient, unstructured data (emails) with strict auto-expiration, guaranteed deletion, and cost efficiency, all under the inherent unreliability and abuse vectors of SMTP.
Mid-level signals3
Senior signals5
Red flags4
3 tradeoffs and 3 stress tests locked
Interview prep
Unlock the interviewer X-Ray rubric, tradeoff matrix, stress tests, clarifying questions, and key concepts.
Design a temporary email service
SMTP Protocol and MX RecordsDistributed Message Queues/StreamsNoSQL Databases with Time-To-Live CapabiliObject Storage with Lifecycle PoliciesRate Limiting and Abuse Prevention Strateg
Design a Disposable Email Service with Auto-Expiring Addresses
Design a receive-only disposable email service, similar to "10-minute inboxes," that issues auto-expiring email addresses and displays received messages via a web UI and REST API.
Functional Requirements
- Ephemeral Address Creation: Allow users to create temporary email addresses that automatically expire after a specified duration (e.g., 10 minutes).
- Email Ingress: Receive inbound email over SMTP and make messages available for display in near real-time.
- Message Management: Provide functionality to list, read, and delete messages via both a Web UI and a REST API.
- Quotas and Rate Limits: Enforce per-inbox and per-user/IP quotas and rate limits to prevent abuse and manage resources.
Non-Functional Requirements
- High Availability: Ensure high availability for SMTP ingress and message reads. Eventual consistency is acceptable for message indexing.
- Low Latency: Display new messages with low latency, targeting a p95 of less than 2-5 seconds from SMTP acceptance to display.
- Scalability: The system must scale to handle millions of inboxes and millions of messages per day.
- Privacy and Security: Maintain strict privacy and security standards, including compliant deletion of messages upon TTL expiration.
- Cost Efficiency: Implement cost-efficient solutions, particularly concerning storage lifecycle management.
Key Areas for Discussion
Your design should provide a clear, high-level overview and specifically address the following aspects:
- Requirements and Public APIs: Define the core APIs for operations like creating an inbox, listing messages, retrieving a specific message, and deleting messages.
- Address Generation and TTL Semantics: Detail how ephemeral email addresses are generated and how their time-to-live (TTL) is managed.
- SMTP Ingress: Describe the setup for MX records, the behavior of the inbound Mail Transfer Agent (MTA), and the email acceptance policy.
- Spam and Abuse Controls: Outline strategies to mitigate spam and prevent service abuse.
- Storage Schema and Indexing: Propose a storage schema for inboxes and messages, including how per-message TTL is handled and the indexing strategy for efficient retrieval.
- Message Retrieval: Explain the mechanism for retrieving messages via the Web UI and REST API, including the authentication model or use of capability tokens.
- Rate Limiting and Quota Enforcement: Detail how rate limits and quotas are implemented and enforced.
- Privacy and Security: Discuss measures for inbox isolation, link-safety within messages, and handling of attachments.
- Compliance and Deletion Guarantees: Describe how compliance requirements are met and how deletion upon TTL expiration is guaranteed.
- Background Cleanup Processes: Outline the processes responsible for cleaning up expired inboxes and messages.
- Observability: Detail the approach to metrics, logs, tracing, and alerts for monitoring the service.
- Capacity Planning and Cost Controls: Discuss strategies for capacity planning and mechanisms for controlling operational costs.
Architectural Considerations
Consider the following architectural elements in your design:
- High-level Architecture: A typical flow might involve an MTA feeding into a queue/stream, processed by a message processor, stored in a durable store, potentially cached, and then exposed via an API/UI.
- Data Model: Define the entities for inboxes, messages, and attachments, along with any necessary indexing entities.
- Consistency vs. Availability: Discuss the trade-offs between consistency and availability, particularly for SMTP acceptance, message availability, and deletion.
- Scaling Strategies: Detail how the system will scale to handle millions of inboxes and messages daily.
- Cost Control Mechanisms: Elaborate on strategies like storage lifecycle management, attachment size limits, and rate limiting to manage costs.