> Even if you don't use Google Apps it's also not possible to have own XMPP address that happens to look the same as an e-mail address that Google knows about (even if it's non-Google address and non-Google XMPP). When they see it they route GTalk users' messages straight to GMail chat, bypassing XMPP.

This stops happening if you disable Talk+Hangouts from the admin panel: https://admin.google.com/AdminHome?fral=1#AppDetails:service...