your subject does not explain the issue. what is a concrete users?
Some account in OpenFire Server. One must not to get he inbox broadcasts messages.
the one may define a privacy list and block incoming broadcast messages.
If you want to manage this on server side you could try the Packet Filter Plugin, anyhow I don’t know whether it suit your needs.
tell particularly, where I must setup in PSI or in the Packet Filter Plugin
visit http://www.igniterealtime.org/projects/openfire/plugins.jsp or https://yourserver:9091/plugin-admin.jsp to take a look at the plugins.
have no idea how to use a privacy list within PSI.