I liked the article as I once had a similar requirement! My approach was that I built a full service that did this including being able to plug it into SES/Sendgrid for sending and ability to add custom props etc... But then my other startup succeeded so I mothballed it.
If anyone's interested, reach out!
Curses to whoever made html emails a thing. What really is the matter with plain text?
It's amazing to me that poor developers are still having to deal with email quirks. I was coding html emails in tables when I started 10+ years ago. It seems as though tooling may be better but the underlying client support is still drastically lacking. Why haven't standards body agreed upon a subset of html/css to be supported by email clients? perhaps they have and I'm unaware? I guess the issue with email is that there is so much more market fragmentation than browsers... It's just crazy to me how bad email clients support is for rich media, and how many people still rely on it as primary source of communication over newer technologies.