You can build a reliable notification system with a team of one by setting up routing and preferences, which is crucial for dynamically sending notifications to users at the right time and frequency. To achieve this, you need to consider multi-channel support, choosing the right API providers, designing user preferences, and implementing an algorithm that routes messages between channels and providers. It's essential to provide granular control over notification preferences, allowing users to opt-in or out of specific channels, frequency, timing, and topics. When building your routing service, choose technologies that can handle asynchronous programming and state tracking, such as serverless technology like AWS Lambda. Additionally, ensure compliance with applicable laws, including the CAN-SPAM Act for commercial email messages and the TCPA for SMS marketing. By following these steps, you can create a notification system that drives user engagement and optimizes cost.