Seven postboxes in villages surrounding Chelmsford were damaged by fireworks on the same day.
Boxes in Stagden Cross and The Street in High Easter, Bakers Mead in Great Waltham, Ingatestone Road in Highwood and Mill Green Road in Mill Green had the explosives fired from them on January 7.
Essex Police are appealing for witnesses who may have seen any of the incidents, which are thought to have taken place between 2.30pm and 11pm.
Officers also want to speak with the driver of a black and yellow Vauxhall Astra seen in High Easter at the time of the incidents.
Anyone with information should contact police at Chelmsford by calling 101.