Google Meet, formerly Google Hangouts, formerly Google Chat, started life as just an XMPP server that Google ran and attached to GMail accounts. (Facebook Messenger was XMPP, too; at one point, it was possible to open up GMail and send a message to someone that was on Facebook. This was before "silo" was the only option.)

After a while, Google silo'd their XMPP server: you could still (at least for a while) log into it using a regular XMPP client, but you could only talk to other GMail accounts. Google cited "spam" as the main reason, but the reason was obviously closing the ecosystem.

Look. Please, hear me out: we can eliminate most of the spam on the internet if we convince Google to turn its email service into a silo. Think about it. And if they do it, maybe it's possible to convince Microsoft to wall off Hotmail/Outlook/whatever. Think about this.