Gotta "nope" this one on legal to carry in parking lots of USPS.
The article you linked was from 2013, where U.S. District Court Judge Richard Matsch ruled it was legal.
However, this was appealed and in 2015 the 10th U.S. Circuit Court of Appeals in Denver ruled against Tab Bonidy by 2 to 1.
The Supreme Court was petitioned on this case and the petition was denied in 2016.
https://www.supremecourt.gov/Search.aspx?FileName=/docketfiles\15-746.htm
THAT SAID...will more recent Supreme Court rulings on the Second Amendment have an impact on this? Perhaps. I would certainly entertain the opinions of others on this.
But right now, 36CFR232.1 Conduct on Postal Property is still in effect:
(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.
The punishment under this code is:
(p) Penalties and other law.
(1) Alleged violations of these rules and regulations are heard, and the penalties prescribed herein are imposed, either in a Federal district court or by a Federal magistrate in accordance with applicable court rules. Questions regarding such rules should be directed to the regional counsel for the region involved.
(2) Whoever shall be found guilty of violating the rules and regulations in this section while on property under the charge and control of the
Postal Service is subject to a fine as provided in
18 U.S.C. 3571 or imprisonment of not more than 30 days, or both. Nothing contained in these rules and regulations shall be construed to abrogate any other Federal laws or regulations or any State and local laws and regulations applicable to any area in which the property is situated.
And the USPS also posts signs saying violators are subject to 18USC930 for penalties for carrying IN the post office. This is a much more significant infraction.
Oh...and how does the USPS define their property you may ask? As follows:
(a) Applicability. This section applies to all real property under the charge and control of the
Postal Service, to all tenant agencies, and to all
persons entering in or on such property. This section shall be posted and kept posted at a conspicuous place on all such property. This section shall not apply to -
(i) Any portions of real property, owned or leased by the
Postal Service, that are leased or subleased by the
Postal Service to private tenants for their exclusive use;
(ii) With respect to
sections 232.1(h)(1) and 232.1(o), sidewalks along the street frontage of postal property falling within the property lines of the
Postal Service that are not physically distinguishable from adjacent municipal or other public sidewalks, and any paved areas adjacent to such sidewalks that are not physically distinguishable from such sidewalks.