The article is good, but misses an important point (that adds yet another confusing thing about email): the difference between Header.From and Envelope.From and

The article is good, but misses an important point (that adds yet another confusing thing about email): the difference between Header.From and Envelope.From and how DMARC also solves this by requiring identifier alignment. Without it, generally only partial validation of the envelope address happens by i.e. SPF.