U.S. Postal Service spokeswoman Augustine Ruiz told the San Jose Mercury News that the powder turned out to be a harmless herbal remedy from Vietnam that a man had ordered for his child.
Ruiz didn't immediately know the name of the substance.
Fire officials say two employees had complained of sore throats and headaches after being exposed to the package around 8 a.m. Tuesday.
Gutierrez says those two, as well as a third employee in the area, were decontaminated by a hazardous materials unit.
The post office reopened by 10:30 a.m.
