The contents of a mail collection box outside the Sanford Post office were deliberately set on fire sometime last night, postal officials said this morning.

A lit match or similar object was put into the collection box, destroying most of the mail, a spokesman said.

“An employee opened (the collection box) up at 5 a.m. and it was still smoldering,” said Tom Rizzo, district communications coordinator for the U.S. Post Office.

Sanford firefighters put out the fire and no one was hurt, he said.

Any mail put in the box after 5:20 p.m. may have been destroyed, according to a notice on the front door of the postal office.

“We are working to identify remnants of damaged mail pieces so we can return them to the senders, who can make arrangements to ensure timely business transactions or personal correspondence ... Please inform your friends and neighbors of this incident so they, too, can make appropriate arrangements,” the notice read.

It was unclear how many pieces of mail were in the box at the time.

“Most of that mail was severely damaged and some of it was completely destroyed,” Rizzo said. “It’s impossible to tell how many were destroyed.”

The fire is believed to be an isolated incident, Rizzo said.

Agents from the Office of Inspector General are investigating the fire, working with local officials, Rizzo said. Anyone with information is asked to call 1-888-877-7644.