Jabber conferences. How to make,but external join?

I worked out how to make a conference room. Despite the Wiki being wrong as usual, the “server” when joining a conference is the same as your jabber domain EXCEPT if you have a subdomain in your username/jid it is conference.jabber.subdomain.example.com" and connecting to your Jabber server is just your domain name, example.com NOT jabber.example.com

Now I have created a room. But my gmail user can not join it. What up?