@Override
        public boolean wantsStanzasSentBy( @Nonnull MUCOccupant sender ) {
            if ( FMUCMode.MasterSlave == mode ) {
                return true; // always wants stanzas - if only because the data needs to be echo'd back.
            }

            return super.wantsStanzasSentBy(sender);
        }
A list of stanzas that need to have been echo'd by a remote FMUC node, before they can be processed locally.
This collection _does not_ include stanzas needed to set up the initial join. This collection is only used
for subsequent stanzas that are shared in a setting where echo-ing is required (due to the mode of the
federation being defined as 'master-slave').
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/FMUCHandler.java