Why are payments mailed to a Manchester Post Office Box?

In the 1980's, the city began using lockbox.  Lockbox is a processing system where a financial institution's (a bank's) employee  picks up the City of Concord's mail from the Manchester post office.  The Manchester post office is utilized because it is a hub, a central post office.  Bank employees prepare the deposit, and forward an electronic file to the city.  Payments are then uploaded to the customer's accounts.  With the volume of payments received at payment due dates lockbox is the fastest method to process payments.