So instead of delivering to every house every day, deliver to every house every other day.
That way they only have to work six-hour days, six days a week.
Ah, I see what you mean now. Interesting idea. That might work, especially for junk mail, although they’d still have to deliver packages every day. They say the package deliveries are what consumes so much time.
My mail lady seems to sometimes work ten hour days, judging by how late she gets here in busy times/bad weather, etc.