Owl Postal Service

Owl post was a wizarding system of sending messages or items using owls as the carriers. Besides the Owl Post Office, individuals and organisations with their own owls used them as their mail bearers — owls were employed by wizards in such numbers that was estimated that virtually all of them were either the property of the Postal Service or individual wizards.
Owls were also used for institutional deliveries, they were delivering newspapers such as Daily Prophet and the owl always had a pouch which it used to collect the payment. 
Owls were also used by some businesses for Owl Order Service, to deliver goods. This service is often used by Fred and George Weasley to deliver Love Potions to their shop placed on the Diagon Alley.