"Mailman" is not an official name yet. It may have been referenced in the storyline as such, but has not been officially named. Alternatively, it may be a name popular among fans, but has no official basis.
The mailman is a jolly old man who speaks his "D" sound with more emphasis. He is passionate about doing his job, saying he would be delighted to deliver the friendship cards, as shown in "Pups Save Friendship Day".
The mailman is a light-skinned adult male who slightly resembles Nintendo's "Mario" in appearance. He appears as an older man with blonde hair, blonde mustache and green eyes. He wears a light blue short-sleeved shirt, which is tucked inside his dark blue short pants. He also wears a blue cap, long socks and a pair of gray shoes.