Decked out in the 153-year-old institution's trademark yellow, Milan's stock exchange gave the post office a warm welcome initially but investor interest flagged early on, with shares edging up at the start before trading flat at their IPO price.
Poste Italiane's chief executive Francesco Caio rang the bell at the symbolic start of trading before welcoming a "new phase" for the company, founded in 1862 after the unification of Italy and boasting 143,000 employees today.
"This is a very important day," said Fabrizio Pagani, adviser to Italy's economy minister on privatization. The flotation was being seen by the government as a test for the rest of Italian Prime Minister Matteo Renzi's privatization drive.
The youthful Renzi hopes the sell-offs will help attract foreign investors to a country slowing emerging from recession.
The post office was floated with an IPO price of €6.75 ($7.46), a move analysts said was aimed at ensuring a good return on investment, with particular interest expected from those betting on Italy's economic recovery.
The company has annual sales of €28.5 billion and 32 million customers. It made a net profit of €1 billion in 2013 and €212 million last year, the slide attributed to one-off restructuring charges ahead of privatization.
Its status as a trusted brand in a financially conservative country has seen it acquire €420 billion in savings deposits through its post office accounts and it has plans to substantially develop its asset management activity.
The government put 38.2 percent of the Poste Italiane up for sale, with about one-third reserved for individuals and the group's employees - of whom more than 26,000 have sought shares. The rest remains in the hands of the state.
The sale is expected to bring in as much as €3.4 billion for the government, but will make only a small dent in the country's debt, which stands at €2.2 trillion.
Following the post office, Italy is set to sell off part of the traffic controller Enav and Italian state railways (FS), with the listing of the latter set for "the second half of 2016", Pagani said on Tuesday.
Smaller sell-offs last year saw stakes in shipyard operator Fincantieri and telecoms group Rai Way floated.