As a stamp collector this article is interesting.
Unlike modern postal systems (which first began issuing postage stamps in 1840) , where the sender typically pays with a stamp, payment for 16th-century mail was often complex and varied, with many systems requiring payment upon receipt or through pre-arranged contracts.
The payment upon receipt by the recipient system failed for the obvious reason: Many deliveries were refused, leaving no one to pay for the service--which may have taken many days and several forms of travel to complete the delivery.
Don in SoCal