public void routingFailed( JID recipient, Packet packet )
    {
        Log.debug( "IQ sent to unreachable address '{}': {}", recipient, packet.toXML() );
        final IQ iq = (IQ) packet;
        // If a route to the target address was not found then try to answer a service_unavailable error code to the sender of the IQ packet
        if ( iq.isRequest() )
        {
            sendErrorPacket( iq, PacketError.Condition.service_unavailable );
        }
    }
Notification message indicating that a packet has failed to be routed to the recipient.

@param recipient address of the entity that failed to receive the packet.
@param packet    IQ packet that failed to be sent to the recipient.
xmppserver/src/main/java/org/jivesoftware/openfire/IQRouter.java