From: (and entire regulation can be read here)
39 CFR 232.1 - Conduct on postal property. | LII / Legal Information Institute
CFR › Title 39 › Chapter I › Subchapter D › Part 232 › Section 232.1
39 CFR 232.1 - Conduct on postal property.
§ 232.1
Conduct on postal property.
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(l) Weapons and explosives. Notwithstanding the provisions of any other law, rule or regulation, no person while on postal property may carry firearms, other dangerous or deadly weapons, or explosives, either openly or concealed, or store the same on postal property,
except for official purposes.
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I'm not an attorney and there is some question as to whether or not carrying a gun for self defense fits the definition of
except for official purposes but, at this time, the Post Office regs consider sending a firearm through the mail to be using the mail services and is "official business".... but does not consider carrying a gun for defense as "official business". I'm guessing because there isn't any "business" being conducted involving the gun.
There is a court case challenging the ban of firearms not involving "official business" on Post Office property but, to the best of my knowledge, it hasn't been resolved yet.
Lawsuit Filed Against Post Office Gun Ban
So my non lawyerly interpretation of all of that is.... yes, a person can carry a firearm into the Post Office for the purpose of sending it through the mail (official business) but cannot carry a firearm into the Post Office to do any business that doesn't involve the firearm.
I would
strongly suggest that anyone who is thinking of carrying a gun they aren't actually sending through the mail anywhere on Post Office property (including parking lot.. or even leaving your gun in the car in the parking lot while running in to pick up the mail) to consult with a real attorney (not faceless posters on the internet.. including me) and get an actual legal opinion.