Australia Post boss Christine Holgate has warned losses for the company's letter business could double in the current financial year and force the postal service to close multiple community branches.

The government-owned company reported a 70 per cent decline in net profit after tax for the past financial year, coming in at just $40.6 million, which it blamed on a significant decline in its letter business.

Falling letter volumes and no price increases in stamps led to a 9 per cent drop in letter revenues to $2.2 billion from $2.43 billion last year, with Ms Holgate warning the losses would likely continue.

"Profit went down $175 million, giving an overall loss of around $190 million. Imagine if the volumes go down close to 10 per cent again this year, which we expect them to because that’s what we’re seeing in other countries," she said.