Optus sent two emails about its triple-0 outage to the wrong public service email address, where they sat undetected for more than a day.

The revelation came at an estimates hearing on Tuesday, where officials from the infrastructure department told senators the telco had used an address that was phased out a week before the outage.

The emails were sent at 2:45pm and 2:52pm on the day of the outage, on Thursday, September 18.

Optus said it had detected and then fixed a triple-0 outage that affected 10 calls, and that it would conduct welfare checks on those affected.

It later emerged that 600 calls had failed and three people had died. The media regulator, the Australian Communications and Media Authority (ACMA), is investigating whether Optus breached the law.

The Thursday emails wer

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