Hackers have hijacked another 1500 email accounts of Telecom customers over the past two days as part of a cyber attack which began almost three weeks ago.
Some 88,500 customers have had their Yahoo! Xtra accounts misused to send spam emails.
Telecom said on Wednesday latest customers affected will have to change their password on their next log-in.
The company said the latest breaches were higher than usual - but on any given day up to 100 accounts are compromised for various reasons.
Telecom said Yahoo! Xtra had assured it the accounts have been hijacked only to send spam, rather than to steal personal details.
Yahoo! is still investigating the cause of the original security breach which happened from 9 February.
A prominent internet lobbyist says it is time for Telecom to dump its email service altogether.
The Telecommunications Users Association is alarmed that still more people's accounts are being found to be compromised.
Chief executive Paul Brislen says Telecom needs to cut its ties with Yahoo!, saying customers don't place so much importance on email anymore and it could be a good time to stop providing the service.
Mr Brislen said alternatively, Telecom could bring the service in-house.