[ascagnel_]

They definitely X-ray parcels, for security. Shortly after 9/11, I remember a local post office failing to detect explosives and it getting reported on; this was notable for two reasons:

- one of the hijackers had received a knife through the mail, and it had been processed through that office, so there was extra scrutiny at the time

- a few years prior, that office processed and delivered a package the Unabomber sent that killed someone

[speakfreely]

The majority of mail screening these days is to find illegal drugs. However, given that so many drugs get through, it seems they only x-ray a small subset.

[dimitrios1]

Yes, the USPS started scanning packages and letters since the great Anthrax scares. This is just a productization of an already widespread, in-use technology.