How to prevent comment moderation flood?

I'm a OS administrator rather than a WP administrator, and i found that one WordPress installation sends an email every single time a spammer tries to post a comment. This is flooding the email daemon and is almost as bad as allowing spam.

I think we could disable comment moderation notification emails, but we don't want to do that.

Is there a way that WordPress may limit the rate at which sends email moderation notifications? (Like, for example, one per hour).