If monthly invoices / packages are based on a monthly volume allowance basis, it would be useful for whomever owns the budget on the account to be notified when they're approaching their usage allowance.
This could come in a form of an automated notification of some sort or a visible barometer of some sort on the Dashboard where it states how many emails have been sent. This could also change based on the time frame selected. For example, if looking at 30 days, what the 30 day allowance is, and if looking at a 12 month period, it would update the allowance to the same time period.
Perhaps the notification is only visible or enabled at a certain % of the the allowance. Most of the time, as long as the volumes are within the monthly allowance, there is no need to monitor it. It is only usually required if it is nearing its limit, as a prompt, for those managing budgets to be aware of the potential increases coming up.