Remember when trains like the SWC would have three or four baggage cars up front full of express and priority mail packages? It helped LD trains near breakeven or better in some cases. Then someone at Amtrak got stupid and started attaching box cars and adding dwell and switching time to the trains, and oh yeah, the "freight" railroads did not like "passenger" trains carrying "freight" cars. Something about competition. But in the beginning it was a succesful program, what changed? FEDEX and UPS taking over moving mail for the Post Office?
Amtrak should be focused on Passenger rail. Adding mail slows down train speed and loading times. If rail was used for mail, it should be done by the freight railroads. I believe USPS stopped using rail for mail altogether.
The old mail sorting center by NYP is being reused as a train hall for customers and that is a more effective and productive usage than reactivating it as a sorting and distrubition center like before where mail was shipped on trains.
The distribution model likely has some carriers perhaps UPS Ground or others outsourcing parcels to freight railroads for ground based services, If train parcel shipment is competitive then carriers would still use it as an option. Airplane has lots of capacity to load on mail in cargo holds on passenger and cargo airplanes. And dedicated vehicles are owned and operated by USPS so they control their own costs and schedules.
Train really is only an option for larger parcels shipped by services like UPS Ground or other shippers who ship parcels to postal addresses who utilize the freight railroads. USPS’s non first class parcel shipment ground products could use rail if it was cost effective but I am not sure if it used freight railroads on these. If i was shipping non time intensive large parcels, train could be utilized as an option if pricing was more competitive.
Ship can handle less time sensitive large items from abroad or coastline distribution. Rail can handle larger packages as can truck and even plane to some degree domestically where these will compete against each other.