Hello Paulo.
Now, i’m in the same situation. And expected exactly the same trouble.
I’ve made some debug job and found that server A thinks that domain of server B is it’s own domain and don’t want to route message outside.
Also in “Server Sessions” there is only one record about “Incoming” session from Server B. It was added when Server B sends messages to Server A.
The next one trouble that I have exactly the same usernames on both domains. But now it’s not the root of issue. I’ve try to send messages to faked users in domain B and server A try to route it localy. =(((
Do you have a fix for this situation? May be we need send a bug report?