After having had a very productive Sunday, I seem not to be able to stop doing stuff
So I started playing with chat.facebook.com (Facebook’s XMPP Server).
Having read P1’s article that Facebook would be using Ejabberd made me curious, as I don’t believe Ejabberd would scale anywhere near the needs of Facebook.
So I investigated the XML responses, and got a hint by Artur that the message IDs look nowhere near the message IDs of any server.
Now, if Facebook would’ve used an existing piece of code, they wouldn’t rewrite the message ID generation. That would be useless.
So, I checked every server I had access to, and I can say, it doesn’t behave like: Tigase, M-Link, Ejabberd, Jabberd14, Jabberd2, Prosody and Google’s XMPP Server.
Thus my conclusion: They have written their own XMPP server.