Thanks for the info, everyone!!! Very interesting. Glad I asked.
And, for what it's worth, here's what the USPS says about Parcel Select on its website:
"“Parcel Select” is the registered trademark name for the Postal Service’s economical ground delivery service for packages entered in bulk, including those entered at destination facilities. It is designed for and generally used by large- and medium-sized parcel shippers. Parcel Select mailers pay postage that reflects the degree of work-sharing they do in presorting their parcels and/or drop shipping their pieces at a destination facility located closer to the delivery point. Mailers are responsible for transporting their Parcel Select pieces to a destination bulk mail center (DBMC), destination sectional center facility (DSCF), or a destination delivery unit (DDU) for business and residential delivery.
In today’s competitive parcel market, Parcel Select service provides very competitive pricing. It is often used by other private parcel companies to complete delivery of the “last mile” for their shipments — particularly for deliveries in non-metropolitan or rural areas because the Postal Service is the only carrier that offers delivery to every door 6 days a week. In fact, a significant amount of the current destination-entry Parcel Select volume tendered to the Postal Service comes from parcel shippers who have traditionally been our competitors: DHL, FedEx, and United Parcel Service (UPS).
Parcel Select service allows each carrier to leverage their core capabilities, such as long-distance transportation, with the Postal Service’s extensive delivery network to achieve cost savings and improved service. Parcel integrators and consolidators offer up-front estimates on delivery times and value-added services, including customized rates and services, billing, manifesting, insurance, tracking, Electronic Data Interchange, Delivery Confirmation™ service, and pickup service. Working together, we have a shared interest to provide improved satisfaction to our shared customers, the originators of the packages."https://about.usps.com/postal-bulletin/ ... 2_002.html
Amazon, FedEx, UPS, DHL, etc., use Parcel Select by injecting at the DDU (local post office) or sometimes the regional center. The point is that they do the line haul themselves. It appears from this that a large shipper could invoke Parcel Select by presorting and having the Postal Service do more than just the last mile, but it is still the mailer's responsibility to get the parcels to the nearest network node at whatever level of aggregation they choose (e.g. sectional center (very aggregate) or local post office (most granular), with doing it to DDU level, if you have the volume, providing the savings that make the operation financially-advantageous to the major players that use it.