Who invented mail letter drop box?

The letter drop box was invented in 1973 by Robert Spencer who worked for Dow Chemical in Midland, Michigan. Their concept was to deposit funds from customers as soon as possible then Dow would turn around and "loan" out short term (like a weekend) funds for large corporations for purposes like meeting payroll. They made tens of thousands of dollars from a lot of "weekend loans."

If they had a customer who mailed funds from Oregon, they were given an address to a lock box close enough so the payment would reach the box within one day. Courriers would visit each box multiple times a day and deposit the funds in a Dow Chemical account.