The telco first reported the matter on Monday afternoon, revealing issues were affecting some users trying to access BigPond/Telstra Mail via the web.

“Our team’s on it, and we hope to have you back in your inbox soon. Using an app to access your mailbox (Outlook) may help in the meantime,” the company said in a social media post.

Telstra later revealed that while it was initially thought customers could use apps like Outlook to access their inbox, that was no longer the case.

Just before 7pm, the telco declared Telstra Mail was back online and customers should be able to access their inbox again via the web or apps like Outlook.

“It may take a little longer for some emails to be delivered, but none have been lost. Thanks for sticking with us while we got it sorted,” Telstra posted.

However, in an update on Tuesday morning, it was revealed some customers were “still facing issues” accessing Telstra Mail.

“Our team's continuing to monitor and investigate. As a first step, we recommend attempting to reset your password and then accessing your account using webmail,” the update read.

“If this isn't successful, please reach out to us by calling or messaging us via the My Telstra app or website.”

A Telstra spokesperson said a password reset would be required for many of the customers still impacted.

“We have seen some customers using third party apps like Outlook facing issues logging in,” the spokesperson told SkyNews.com.au.  

“In many of these cases, a password reset has fixed the issue.

“We’re continuing to monitor and investigate. Our support team are here to help via phone or message in the My Telstra app or website.”

Disgruntled customers lashed out at the telco in the comments.

“Provide the service we are paying for don't put the problem on us,” one angry user said.

Another slammed the matter as a “joke”.

“You've not told people (WHO PAY YOU) what the issue was and now you're forcing people to reset passwords,” they said.  

One frustrated customer told 2GB his transport business had been affected since Monday afternoon.

“I couldn’t send invoices, nothing,” he told the radio station on Tuesday morning.

“I’m in a jam, I’m stuck.”