XMPP server-to-server - traffic optimization?

I'm working on a design for a xmpp chat solution which involves some servers and where at least one s开发者_开发知识库erver is connected with serious bandwidth limitations.

Assuming, we have two servers A and B, some users 0..n connected to Server A and some conferences 0..m provided by Server B.

Now assume, some users enter a conference room and a message is sent to that room. Will

1. Server B send this message once to Server A and Server A distributes it to the users or will
2. Server B send this message to each individual user of Server A?

According to the protocol spec, XEP 045, multi-user chat messages are reflected independently to each participant. I can't tell on a brief read if it is legal to send them server-to-server without reflecting. However, it might be worth asking this question on an xmpp.org mailing list, where the experts tend to hang out.