Were the armed personnel stationed in the Polish Post Office normal civilian postal workers, or were they trained members of the Polish armed forces or paramilitaries who had been smuggled into Danzig in the guise of postal workers?
As I understand it, the role of the Polish Post Office in the plans of the Polish military high command was that of a Polish armed fortress on Danzig territory, which in the case of hostilities had the mission of holding out and pinning down as many enemy personnel as possible until the arrival of the large Polish forces which had been stationed close to the border of the Free City, for the purpose of moving in and occupying it.
In the event, the Polish plan proved to be counter-productive. The Polish forces stationed close to Danzig with the mission of occupying it were all cut off and destroyed.
When I was a university student in the 1960s, I worked at the main Sydney post office every Christmas holdidays. We were taught how to sort letters, but were not given weapons training.
A particular point regarding the Polish post office is that the Germans themselves used their own non-military, uniformed servants of state in a war crime by having the Danzig fire brigade pump gas into the post office. Definitely a case of double standards!
Presumably if the Poles had won the battle of Danzig, even if temporarily, they would have executed those members of the Danzig fire brigade.
It is interesting that in April 1943, the Warsaw fire brigade (presumably staffed by ethnic Poles) was an integral part of the force under Stroop that suppressed the Warsaw Ghetto uprising. Firemen in their characteristic brass helmets can be seen in the background in the iconic photos of Stroop observing the burning of the ghetto.
I guess Polish firemen would have had few qualms about taking part in a bit of Jew-busting.