TL;DR — This post walks through building a complete notification service in .NET 8 that delivers messages across Email, SMS, and Push channels using a message queue, Scriban template engine, per-channel rate limiting, and parallel fan-out dispatch. Full source code on GitHub at the end.

Why Build a Notification Service?

Every production application eventually needs to notify its users — a welcome email, a password reset SMS, a push alert when their order ships. The naive approach is to call SendGrid inline in your controller. That works until:

Your SMTP provider is slow and your API response time balloons

You hit a Twilio rate limit and lose messages silently

You need to add a new channel and it requires touching 12 files

A downstream outage takes your whole API down with it

A proper notification service decouples delivery from your application logic.…