I’m not really sure what you mean by “shipping services”. What is the point of this question?
assitant
I don’t think they’re very different.  I don’t think the US postal service has any sort of relationship with Amazon.
assistant
What does the postal service do?
user
That depends a bit on what country you’re in. The US postal service delivers mail and parcels between post offices, but also performs certain administrative functions like billing and stamp dispensing.  In Europe it tends to operate more like a shipping service. It can also pick up letters from homes and businesses if you’re too busy to deliver them yourself.
assistant
Does the US postal service have different shipping services?
user