UPS and Fedex have operating margin of ~6%. They have spent 10's of billions of dollars into optimized sorting facilities and logistics. Yet, Amazon uses USPS for last mile delivery. USPS also has to deliver to non-profitable remote locations and has public unions which demand above-market salary/pensions. A less-optimized player with higher cost base offers service at lower cost than a business with 6% operating margin - simple math makes me believe they are losing money on those orders.
Why is this? Did the USPS have some kind of retirement funding scandal, or was someone trying to smother it?
Interestingly enough by eliminating the daily delivery of mail also kills the DMA business, which while everyone hates spam mail, is still a vital business tool for small and local businesses. Fedex will not deliver mail to your house that costs a nickel.
FedEx will deliver mail for a nickel when they get a dollar from the government to do so.