Not all emails being sent to and from businesses that are Telecom customers are getting through to recipients.

A company in the Bay of Plenty said the problem began on Friday and it believed it was missing hundreds of emails.

It said it had been advised that some Xtra email servers had been blacklisted because of spam.

It believed the problem might be widespread but because failed emails were not bouncing, businesses and their customers that had been hit might be unaware of the fault.

Xtra confirmed on its website that there is an issue affecting customers that use Telecom's Officemail platform for emails and it said it was working to resolve the problem.

It said the fault was preventing the sending, and delaying the delivery, of mail, but made no mention of the possibility that the nature of the fault might mean businesses and their customers might not be aware of the problem.

Similar spam-related issues have affected TelstraClear's email service on at least two occasions in the past. In its case, no emails were lost but they were delayed by up to a few days.