@Override
    public Iterator<String> getFeatures() {
        return switch (type) {
            case store, store_and_bounce, store_and_drop ->
                // http://xmpp.org/extensions/xep-0160.html#disco
                Collections.singleton("msgoffline").iterator();
            default -> Collections.emptyIterator();
        };
    }
Unregisters a listener to receive events.

@param listener the listener.
xmppserver/src/main/java/org/jivesoftware/openfire/OfflineMessageStrategy.java