Any tips to build first-time and returning user email flow for a SaaS platform?

The main thing for the email flow is firstly to get your customer to stick - and usually that's to introduce the user to the product, kind of like an onboarding. After that it's about trying to keep them sticky with product updates, continued use etc.

I am trying to build email flow content to automate. This is the first time and found it confusing. What content and what should be best timeline for welcome email flow?