Doctor Dolittle's Post Office by Hugh Lofting

So the Doctor and Jip and Speedy-the-Skimmer sat down in the shade of the palm trees and for the first time plans for that great service which was to be known as the Swallow Mail were discussed.

"Now, my idea, Speedy, is this," said the Doctor. "Regular foreign mails are difficult for the Fantippo post office because so few boats ever call there to bring or take the mails. Now, how would it be if you swallows did the letter carrying?"