Indeed, there are regional sorting centers that then send to the local post offices to go to the carriers. Although what I find odd is that for residential deli

Indeed, there are regional sorting centers that then send to the local post offices to go to the carriers. Although what I find odd is that for residential delivery, I always get the mail the same day, only at my P.O. Box does the mail sometimes come 1–3 days later. If you look at the email, the promise isn’t “coming today” but “coming soon”.