Emails and text messages released to 9News have revealed the scramble inside Optus after it discovered last week’s triple-zero outage.

The first email was sent to the Federal Department of Communications on Thursday, September 18, at 2.45pm.

An Associate Director at Optus Government Affairs reported that Optus had been notified about issues with triple zero calls affecting some customers in South Australia and Western Australia.

Emails to the Department of Communications suggested that the suspected outage cause was linked to the “Regency Park exchange,” a detail later confirmed by an Optus spokesperson.

“We can confirm that the outage was due to a firewall upgrade at the Regency Park exchange in South Australia, which explains why only certain states and territories serviced by this exchange experienced impacts on emergency calls.”

“Optus advised the Minister’s office of this issue and later provided a further update based on the information we had at the time.”

Optus Chief Executive Stephen Rue has also blamed the issue on human error.

“That’s not an investment issue, that’s people not following process.”

Separately, yesterday Optus faced a $100 million fine for selling products to hundreds of vulnerable customers, including individuals with mental disabilities.

Minister Wells today signalled the company shouldn’t “be surprised to hear” they can expect more significant fines.