The Post office was established in the Constitution (Article I, Section 8). I believe it would take an amendment to the Constitution to get rid of it.
This is what I remember from my 1949 Civics 101 class.
“The Post office was established in the Constitution (Article I, Section 8). I believe it would take an amendment to the Constitution to get rid of it.”
Yup.
http://www.house.gov/house/Constitution/Constitution.html