Ask HN: How do you handle user notifications?

After building >10 web and mobile apps, I realize that I am spending too much time building the same User Notification System in my backend.

By User Notification System, I mean the logic that consists in sending transactional emails and push notifications to users.

It usually consists of (for email): - writing the content of the notification (e.g. HTML/text) - sending the notification (e.g. using a SMTP service such as Sendgrid) - handling unsubscribes (e.g. at bottom of email) - changing the content (often requested by the marketing team)

The same applies to push notifications, SMS, etc.

Is there a faster way to handle this? How do you handle it today?