How do you make a newsletter about a product update and notifications?

Hey indiehackers. I'm thinking about two types of newsletters that newly signed up users should automatically subscribe to and can opt out each anytime.

1. Product updates newsletters. All archives should be publicly available in a blog format. It will be like a substack, but substack doesn't have an API. How do you handle it?

2. Notification emails. They should get a welcome email that contains helpful tutorials, trending emails, or "we miss you. come back." emails. Those emails should not be in public. Normal newsletter system (eg mailchimp, sendgrid) is enough?

If you do it automatically, how would you implement?

Thank you! Hope this thread helps other people like me