[davidw]

[Old man voice] Back in my day these kinds of articles loved pointing out that, well, the email address could be a UUCP address and that's a whole different parsing situation.

Of course, even then in the mid 90ies, UUCP was not something one really encountered outside of "so you think you're going to parse an email address with regexp?!" articles.

https://en.wikipedia.org/wiki/UUCP#Mail_routing

[mesrik]

Oh, and there were more than just UUCP bang paths.

IBM Memo, Novel Netware etc. groupware and such X.400 and routing those required also odd email conventions. VAX VMS addresses did have % left side routing in too.