[horsebridge]

Lists like these would be better with some more explanations for the less obvious bullet points. For instance, when/why would an email have multiple From addresses?

[jaza]

Yeah, that one took me by surprise. I had no idea that multiple from addressees was possible. I wonder how many (popular today) email clients support that (for sending and/or for receiving)?

[umanwizard]

https://serverfault.com/a/554615

Tl;dr it’s intended for messages with multiple collaborating authors, but is rarely used in practice.

[jcla1]

I'd deem it useful, though unusable in practise, as GMail for example does not accept messages that contain multiple From addresses.