Tonton Streaming CatDog (1998) S1E26 - Fistful of Mail!

Dog meets up with a paperboy faster than him. This agravates him, and he trys everyday to get faster. When he realizes that he won't ever be, the former mailmen make a disgrase of him. Then...he relizes that the mailman is a person who has been faster since childhood, and he goes faster than him.