Something not mentioned is the additional security built into the obvious wax seal. So in order to test couriers credibility and trustworthyness to deliver wax

Something not mentioned is the additional security built into the obvious wax seal. So in order to test couriers credibility and trustworthyness to deliver wax sealed parchments, a courier would be required to collect and deliver said parchment in a controlled experiment. So the route would be lined with spies in on the test who could report back anything untoward. The wax seal would be laced with Atropa Belladonna[1] which when inhaled from melted wax would cause the pupils to dilate and the delivery point would be dark. So when the courier handed over the parchment a lantern would be held up to the couriers face to see if the pupils constricted in the light. If the courier had melted the wax laced with belladonna, their pupils would look like saucers and the recipient would know the wax seal had been melted & vapours inhaled. It was a measure to protect against counterfeiting wax seals. I dont think this knowledge made it to the US, but it was very common in Europe. Loyalty & trustworthy tests still go on today, but they have evolved somewhat with the times, but you may not even realise you have been tested! [1] https://www.historyandwomen.com/2012/07/fatal-beauty.html#:~:text=Native%20to%20Europe%2C%20belladonna%20is%20one%20of%20the,state%20of%20arousal%20where%20a%20person%27s%20pupils%20dilated https://www.historyandwomen.com/2012/07/fatal-beauty.html#:~....