This is Spark Support forum. Is there now an “Packet Filter” plugin for Spark? I assume you are talking about that one for Openfire, installed on server side. => Packet Filter Plugin
There is an REJECT action. I have not tried that, but it sounds like it could send back a message. (see Actions --> Reject in above document)
However, I’m developing an similar plugin, which has much more features. You have more “actions” like sending messages, sending emails, automatically ban users and count messages per user. Also there is a branching action so you are not limited to the linear rule processing, it’s a tree like structure. As I said, it’s in development. Basic functions are implemented, but there is currently no user interface. I’m currently working on an XML import/export feature, so you can load, save and share rulesets with other users. I’m developing this in my free time, and there is currently not much of that. It can take months until I can release a Beta version.