Dorsey, a black and white shepard, is the only four-legged mail carrier in the history of the USPS. From 1883 to 1885 he delivered mail out of a modified saddlebag affixed to his back, to the mines surrounding Calico California. He wore special made booties to protect his paws from the hot, sharp rocks on his seven mile roundtrip route.
So valuable was his service that when his owner was offered $500 for the dog, he refused stating, "I'd rather sell a grandson." Dorsey's service was remembered in the 1972 album 'The Ballad of Calico' with his own song, 'Dorsey, the Mail Carrying Dog.' The album is out of print and I have never heard it, but I'm told the song could make a grown man weep.