The MSH Traffic Policy have ability to to track how many emails are sent by particular user.
To enable this feature use Message Count Based on Sender action.
This condition will be true when user firstname.lastname@example.org will send more than 200 emails per day.
When condition is defined it’s time to create action which will be invoked when emails count reach limit. Block Message action with custom message for sender.
After these simple steps, user will be able to send only 200 messages per day.
To learn more visit MSH Traffic Policy website.