I kicked off the notification system design by focusing on scalability and event-driven architecture. Mentioned using a message queue like Kafka for processing notifications, which the interviewer seemed to appreciate.

We delved into aspects like user preferences, different types of notifications, and how to handle failures or retries. I fumbled a bit when asked about the database schema.

My initial thought was to go with a relational database but the interviewer nudged me towards NoSQL solutions, which I had less experience with.