Commonwealth Bank of Australia is reaping the rewards of its "post-box" banking operation in the Mediterranean island of Malta, booking a A$55 million benefit last financial year from lower offshore tax rates, according to The Australian newspaper.

The benefit was almost double its nearest big four rivals, suggesting that the structure set up by CBA in Malta is generating tens of millions of dollars in tax benefits, the newspaper said.

Malta is no longer regarded by the Australian Taxation Office as a tax haven, the newspaper said.

The CBA holding company Newport, which has a $5 billion balance sheet, is domiciled in Malta. Newport, in turn, owns CommBank Europe, which has held a Maltese banking licence since 2005, employing a total of six people, including clerical staff and executives.

CBA chief executive Ralph Norris defended the Malta structure at last Monday's September quarter trading update. Last week, the bank showed a profit of around A$1.4 billion for the quarter to 30 September, buoyed by income growth in wealth management and insurance.