One of Australia’s biggest telecommunication companies sent emails about a deadly outage to the wrong email address at the Department of Communcations where they remained unread for over a day, parliament has heard.

Optus’ emails also underplayed the severity of the 18 September outage, which has been linked to four deaths, including that of an eight-week old baby, as people could not reach emergency services.

The first email was sent at 14:45 that day, and a second one seven minutes later to say it had been fixed and 10 calls were affected. In fact, more than 600 calls to emergency services had failed, over 13 hours.

Authorities only learnt about the outage the next afternoon, more than 36 hours after it began, from the industry regulator.

“That communication… was sent to the wrong address, which we have told industry a number of times is not to be used as a source for notification,” Australia’s Deputy Secretary for Communications James Chisholm said in parliament on Wednesday.

The email address was changed only a week before the outage, but telcos had been told about the impending switch two weeks prior, the federal communications deparment said.

Senators grilled Chisholm on why automatic replies were not set up to inform senders the address has since been made redundant, to which he said that it was Optus that did not abide by laws that require telcos to redirect triple-0 calls to other providers during an outage.

It was a deviation from standard procedures during a routine firewall upgrade that caused the outage, Optus said after the incident.

Australia’s media regulator is investigating whether Optus, wholly owned by Singapore company Singtel, had breached the law.

Singapore’s Prime Minister Lawrence Wong, who is on an official visit to Australia, has apologised and extended his condolences over the incident.

“I understand fully the anger, frustration and outrage at what has happened,” Wong said, adding that it was “tragic” that four people had died because of it.

“From a government’s perspective, we expect our companies to act responsibly, and we will certainly expect Singtel and Optus to comply with the laws and do whatever they can to cooperate with the investigation,” he said in Canberra on Wednesday.

Singapore state-owned investment fund Temasek Holdings holds a 51% stake in Singtel.

Optus has been under intense scrutiny over a series of incidents in recent years, including a cyberattack in 2022 that compromised the data of millions of customers, and a nationwide outage in 2023 which left millions without mobile and internet for up to 12 hours.

Optus’ former chief executive officer Kelly Bayer Rosmarin resigned in 2023 amid criticism over how the telco dealt with the outage.

Its current CEO Stephen Rue is facing similar calls to step down, and some lawmakers have also asked for Optus to be stripped of its operating licence.