> Every email carries two "from" addresses

I made a presentation about exactly the same subject many years ago, but I was not shy of separating the SMTP protocol (RFC 821 and the following ) and the email message (RFC 822 and the following).

It makes the link between SPF, DKIM and DMARC much clearer.

Anyway. The article covers just the bare minimum, and in the most obscure way.

For those interested in the inner workings of contemporary email delivery... I recommend the posts by Alex Shakhov on LinkedIn https://www.linkedin.com/in/alexshakhov/ (Yes, there is still meaningful content on LinkedIn, it's just vanishingly rare)