And more recently how Google dealt with XMPP. I certainly would not want to rely on them not breaking email when it's to their advantage.

Not sure what you mean, but Google Groups is basically enabling ... mailing lists. So we go in circles, back to email.

Google groups was based on Google acquiring DejaNews and building a usenet archive and interface on top of that - mailing lists are a later addition. The usenet interface was (and I guess still is?) terribly broken, making it a pain for other usenet users to deal with posts from google groups users, because it simply works in a way that hinders interoperability with the rest of usenet.

(And while at it: The mailing list feature is also quite defective, obviously built by people who don't really have a clue how email works.)

OK, I understand what you're saying. I'm not really familiar with the history of Usenet and Google Groups it seems.

And for mailing lists it could be better, but as a user of several mailing lists of various open-source projects, I have had no problems.

I am noticing that Google doesn't work in our interests though. For example I am disappointed by their shitty support for IMAP, CalDav and CardDav.