In US, we call them Flea Markets, but in Italy they are known as Mercatini dell’antiquariato. Each town has it’s own mercatino, usually happening on Sundays and on a monthly recurrence. It’s a boon for tourists who want to bring home a piece of contemporary Italian history. Before you leave, try to Google for ‘Mercati fiere’ and add the name of the city you are going to visit. You’ll likely end up with several relevant links to lists of local events you may be interested to attend. Of course, none of these information is in English 🙁
Postmen in Italy know very well their neighborhoods. You can spot them on their Vespa carrying their bags full of mail, quickly get off their motor scooters and ring (twice) every bell until somebody opens the main door of the building. Unlike in US, postmen will not pick up outgoing mail. You have to drop it in those red mailboxes dispersed around the city.