37-year-old Suzanne Muscara was indicted on Wednesday.
According to court documents, the charge arose from an investigation into a suspicious letter processed at the mail sorting facility in Hampden in October 2018.
The documents say the letter was leaking a fine white powder and it contained a threat.
The powder was tested and it did not contain any toxic substances.
If convicted, Muscara could face up to 10 years in prison and a $250,000 fine.