> Wait, what? You could chat from [email protected] on your bespoke xmpp server and send messages to user@gmail without needing a Google account and vice-versa?

For some glorious years between 2006 and 2013 (Hangouts), this was indeed possible. I run my own XMPP server and I used to chat with GTalk users all the time. For literally years.

> They didn't really support federation in a standards compliant way

It was standards compliant enough. In the original RFC, server-to-server TLS was mandatory to implement but not mandatory to enable/deploy. The XMPP community later moved towards enforced server-to-server encryption, but this was many years later and had little impact on GTalk federation during the time that it was supported.

I remember looking into it, and discovering that it didn't work in a sane way (ie: no server tls support). Why would I want to expose traffic unencrypted? Especially considering dangerous content, like attachments etc.

Now I see that Ms allows federation for on-premise lync - but not for office 365. :-(

Everyone wants their own silo, and force their multitude of awful clients on people.

Actually, it still worked for existing contacts until half a year or so ago, when they seem to have silently dropped it completely (I haven't really investigated, contacts I had on google simply moved to other servers, that fixed that).