Sanford police Sgt. David Morgenstern said a Seminole High School employee was putting the 6-inch-by-8-inch envelope into Principal Mike Gaudreau's mailbox when she noticed the foul smell, the Orlando (Fla.) Sentinel reported Wednesday.
Police said the worker and three or four other school employees who touched the envelope while trying to determine the cause of the odor were placed in quarantine until the Seminole County Fire Department's Hazardous Materials team identified the substance as excrement.
"We were concerned at first," Morgenstern said. "You could mask some sort of chemical. We wanted to make sure all the faculty and students were safe."
Morgenstern said the envelope contained a letter with "colorful language talking about the high school principal."
The spokesman said police were investigating and the person behind the letter could face a charge of disrupting a school function.
"There are no real charges for sending a poopy letter," Morgenstern said.