how can stop php mass mailing softs ???

[bsasninja]

I have several rules at exim for max recipientes, emails sent per hour at whm, etc.

But sometimes, stupid customers upload maillist software written in php, to send a massive mail from the server.
Once I know who is sending I delete the account directly.

Is there a rule to prevent that?? Server loads jumps to clouds when mass mailing is done.

Thanks.