Always view couriered letters and communications with suspicion unless they are EXPECTED.
If you are a regular recipient of couriered communication ask your central mailroom what level of security screening, if any, that they afford to communications sent via FEDEX, UPS, DHL, etc., as your welfare and life may depend upon delivered communications.
Typically, suspicious communications transmitted by couriers are worthy of suspicion if they are not expected.
Additionally, letters and packages containing excessive postage, often oily stains, incorrect spelling of the addressee’s name, are lopsided, or bear markings such as “confidential” and “addressee only,” should be afforded special security screening, ideally via X-ray, before being opened.
Unfortunately, in many organizations suspicious communications are not afforded special screening.
As a matter of interest, in December 2007, a letter bomb killed a French secretary and injured a lawyer working in a Paris law firm where French President Nicolas Sarkozy once worked.