It depends whether his house is along his route or somebody else's.

No, SpongeBob, there cannot be an infinite regress of mailmen. That would be like saying an infinitely long train can move without an engine. No, there must be one singular, supreme mailman at the end of the very long chain of mailmen who originates all mail that is ever delivered. A mailman to whom no mail is delivered. This mailman we call Louis DeJoy.

It's very simple. You just use the latest mail direction file (a multi-gigabyte text file, btw), compare it against the portion of the most currently published Labeling List, and depending on the mail piece's 11 digit routing string, mail class, and USPS induction facility, that will determine which individual carrier has whose mail on their route.