Yahoo Xtra customers are again pulling their hair out as email services are disrupted once more.
Some users have been unable to access or properly use their email for up to three days and others have had spam emails sent from their account.
An advisory on Telecom's website asks customers to change their password but some users have complained of being unable to do so.
"Email services have been majorly disrupted now for a third day. I have just been on the phone to their tech support and they have no idea when it will be fixed. They put the blame at Yahoo's feet,'' said a customer named Mike.
"Not only are emails not being delivered to mail client apps, you can't log into it via Yahoo.''
The problem with Yahoo! Xtra is not isolated to New Zealand, with US customers also experiencing difficulties.
In a post to its website, Yahoo! said it was "very sorry'' for the bug which was affecting Yahoo Mail, blaming it on a hardware problem that was bigger than originally thought.
"Some of our users have not been able to access their mail since 10.27pm Pacific Standard Time on Monday night (7.27pm on Tuesday NZT), due to a hardware problem in one of our mail data centres. The issue has been harder to fix than we originally expected.
"We have dozens of people working around the clock to bring it to a resolution. We believe our current efforts will restore our users' access to their inboxes by 3pm PST today (12pm on Thursday NZT).
"We'll post again then on our @YahooMail Twitter handle.''
A spokeswoman for Telecom said it did not yet have an estimated time for when the problem would be fixed, but assured Yahoo! are working hard to fix the issue as quickly as they can.
"We apologise for the inconvenience and frustration that it may have caused.''
One frustrated customer, Derek, said: ''... 36 hours and counting of email outage for the Yahoo!Xtra service.
"I generally have nothing but respect for Telecom's support team - really! - but their lack of communication on this one has been as frustrating as it is atypical.''
A customer notice on Telecom's website apologised for any inconvenience and said: "Our technicians are currently working to resolve this issue.''
On Twitter @MarieJeffriesNZ said: "Hey @TelecomNZ I'm trying to change my Xtra password as instructed & keep getting told to try later. When will I be able to change it?''
While @lucymk posted: "Why is it so difficult to have xtra email @TelecomNZ ? Had 2 change pw last week already, now it won't work on my phone today. #why''
A Telecom spokeswoman said a small number of customers had experienced "some issues'' with Yahoo Xtra email services, but expected the problem to be fixed soon.
"We understand it's incredibly frustrating [for customers],'' she said.
"We apologise and we're working on it to get back up and running as quickly as we can.''
Less than two weeks ago Xtra customers found themselves locked out of their accounts after a wave of spam attacks. A previous spam attack in February compromised around 87,000 accounts.