How can we track the duplicate invoices sent to the customers in AR?

Customers are receiving duplicate Invoices as attachments to their contact mail id's. Because of this there is lot of consuming in validating the exact number of invoices. Client reported that "A couple of years ago, one customer mentioned they could only handle a certain number of transactions per hour. It seems that the majority of increases have occurred over time, which is now creating constraints for larger customers."

Do we have any feasibility to track the duplicate invoices sent to the customers?