What is so hard about reaching conclusions about any of the "mysteries" lies in not having access to the info that the authorities have.
BTW, do you have any idea what the deceased postal workers jobs exactly were? And what kind of machines they were operating, if any?
Everything concerning the dead postal workers has been public for a long time. One of them was cleaning what turned out to be a contaminated machine with a high pressure air hose. I think the other guy was in the same area.
They didn't just inhale a couple or three ~ they got spores by the tens of thousands!