HAZMAT crews were called over the weekend to the Canada Post processing plant in Stoney Creek over fears involving a suspicious package.
Police say a worker at the plant became alarmed when she saw a message written on the outside of the package and an oily smudge on the side.
HAZMAT crews determined the substance on the envelope was some sort of synthetic cannabis oil.
THe post office says it takes the safety and security of its employees and customers seriously.