Microsoft Senior Developer interview questions

Design a notification Service. Should be highly scalable and support multiple notification surfaces like web, mobile push, sms, emails etc. How to handle failure and discuss how to implement Retries in the system. Various questions on the components used such as Cache, Brokers etc.

Hard, not too easy. They gave plenty of time to solve the code but I just wasn't too confident. In hindsight, I should ve been better prepared, But I still would've screwed it up.