Is it possible (with Cpanel/WHM) to limit how many emails a client can send at once?

And/or, what other methods can be used to stop clients from spamming?

Thanks for any suggestions.

DreamHost limits their clients to 500 emails at a time. They don't use Cpanel however

My old admin did something like that to our old server for free clients. Limited them to 10 messages an hour. I'm not sure though, but I've found a few close things on Google.