An abandoned stolen car containing four sacks of unprocessed mail was discovered in the early hours of Monday 27 May on Corso Italia, according to reports in La Repubblica.
Police found over 1,000 letters after searching the suspicious Opel Agila, which was left open with the radio on and keys in the ignition.
All the correspondence had postage stamps affixed but had not been franked by the post office. The letters have been handed over to Poste Italiane which will forward the unopened mail but will return all opened mail to senders.
Police have launched an investigation into the mystery cache of letters but have confirmed that none of the post boxes in the area appear to have been tampered with.
Separately, last March police arrested a postman in Subiaco, to the east of the Rome province, for failing to deliver a substantial amount of mail over a three year-period, in order to return home early. The story came to light after police found dumped bags containing over 200kg of undelivered mail.