Comment by ralphm

As far as I know, Facebook Messenger's XMPP support was only exposed to clients (c2s), not to other XMPP servers (s2s). Microsoft's Lync (now known as Skype for Business) supported XMPP federation until 2019. WhatsApp's client protocol was originally based on XMPP. I'm reasonably sure that both AIM and Yahoo had XMPP server-to-server support ready around 2008, but can offer no proof.