Australia Post has confirmed the sale of one of Australia's most significant heritage buildings, the Sydney GPO, to two Singaporean billionaires, despite an outcry over heritage concerns and a secretive sales process.

The sale stands as one of the last acts of outgoing Australia Post boss Ahmed Fahour who leaves the organisation on Friday, delivering a $150 million bump to the organisation's bottom line.

Sydney GPO has been sold in a secretive deal for $150 million. Credit:Wolter Peeters

Australia Post said Mr Fahour would not benefit from the sale, including from bonuses.

"Mr Fahour's compensation for FY2016/17 is unaffected by the sale of the GPO. His one month of employment in the new financial year (FY17/18) does not have a bonus attached to it," Australia Post said in a statement.