Greeneville police are investigating vandalism between Sunday night and Monday morning at property in the 300 block of Sunset Boulevard.
The homeowner said someone "had placed several fireworks in his mailbox and set them off inside the box," Officer Louis Calobrisi said in a report.
The interior of the mailbox sustained fire and heat damage, the report said.
The homeowner said that several patches of grass in the yard were burned where fireworks were set off.
A neighbor told officers that she saw two young men Sunday night in the area "acting suspicious."
Damage to the mailbox totals $100.