A couple postal workers died about 20 years ago when someone used the U.S. mails as an anthrax-delivery mechanism. Details are here: https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5239a2.htm Note that's there's also a deeper CDC analysis looking at whether mail sorting is a job with higher than usual mortality rates. (Answer: probably not).

Granted, that's a long time ago, and it doesn't happen habitually. But if you're going to have a workforce safety team (good idea), they will likely want to either actually do something to stop the threats, or at least signal to management that they aren't totally clueless