Four former UPS workers have pleaded guilty to conspiracy to sell stolen handguns in what federal officials are calling one of the largest gun-trafficking schemes in the state's history.
The UPS response to its own lack of internal security was to initially ban firearm shipments. They since figured there was a buck to be made, and modified their policy to require that shippers use the more expensive Next Day Air--from one of their shipping centers, not from an "authorized outlet".
American Handgunner did a good synopsis of the rules a few years back.
Here are the current regs for:
UPS
Fed-Ex
DHL
USPS (Sec. 11.1 - 11.4)