Bug in French government’s WhatsApp replacement let anyone join Élysée chats

I'm not a big fan of Postel's law / the Robustness Principle [1] and this is a great example why. Given the email address "anaddress@protonmail.com@presidence@elysee.fr", one piece of code parsed it as "presidence@elysee.fr" and another as "anaddress@protonmail.com". Had either piece of code just rejected it, it sounds like the bug wouldn't have existed.

(Interestingly, validating email addresses is super, super hard and generally not worth it. The one check that does seem to generally make sense is to validate that there is a single "@" in the email address with other characters to both sides - which would have worked great for this case)

[1] - https://en.wikipedia.org/wiki/Robustness_principle