More than 20,000 Telecom customers have had problems receiving emails, after a huge backlog caused by an email the size of 200,000 normal messages.
Telecom spokesperson Jo Jalfon said the single email sent from overseas to a customer on Wednesday was about the same volume as one day's total traffic on the system.
There had been about 600 complaints about the backlog which had affected nearly all Xtra business customers. Some businesses had not received any emails for nearly four days.
"It means that people are not able to receive emails but it's been compounded by the fact that people are trying to resend them because they think they're not getting through," Ms Jalfon said.
She said Telecom had people working round the clock on the issue and hoped everything would be back to normal by Sunday evening.