private Message createServerMessage(String subject, String body) {
        Message message = new Message();
        message.setFrom(serverAddress);
        message.setType(Message.Type.headline);
        if (subject != null) {
            message.setSubject(subject);
        }
        message.setBody(body);
        return message;
    }
Sends a message with a given subject and body to one or more user sessions related to the
specified address. If address is null or the address's node is null then the message will be
sent to all the user sessions. But if the address includes a node but no resource then
the message will be sent to all the user sessions of the requested user (defined by the node).
Finally, if the address is a full JID then the message will be sent to the session associated
to the full JID. If no session is found then the message is not sent.

@param address the address that defines the sessions that will receive the message.
@param subject the subject to broadcast.
@param body    the body to broadcast.
xmppserver/src/main/java/org/jivesoftware/openfire/SessionManager.java