I need to build a notifications service for our application, and it would be nice if one of my existing tools like Intercom provided the service instead. I want

I need to build a notifications service for our application, and it would be nice if one of my existing tools like Intercom provided the service instead. I want to be able to send messages of varying levels of urgency - e.g. "send password reset now" vs. "this message should arrive within an hour and can be bundled." The service already has communication details - email, phone, push notification info, maybe even facebook auth. I wish it would intelligently route to the correct notification method based on each user's responsiveness (did they open the email?), cost (can I save money by using push vs. sms?) and available methods (e.g. I don't have a twilio number in their country). An API for marking messages as read via a UI notification center would be cool too. Message spam is the worst, and building intelligent routing across communication methods is becoming a pain.