Orange broadband customers have been unable to access e-mail accounts for weeks, due to an unidentified problem with the company's e-mail servers.
A callcentre support worker described the outage - which began in July - as a serious problem.
"There are many customers facing this problem. The problem is with the Orange application and the case has been assigned to engineers," he said.
An Orange spokesperson confirmed the problems but said the numbers affected are small. "We are aware that this issue has affected a small number of our broadband customers. We are taking this very seriously, and we have already begun the process to restore the service to those customers who have been affected."
One irate customer, who uses a Freeserve account, contacted Computer Weekly and said she had been trying in vain to get answers from Orange for weeks. "It is very frustrating and worrying because we have several small businesses that rely on the e-mail address that is not working."
The division became part of the Orange group in 2000 when Wanadoo acquired Freeserve for £1.6bn. Freeserve was the UK's largest internet service provider at the time.
The customer said the problem started at the beginning of July and all attempts to communicate with Orange via e-mail and telephone have ended in frustration.
"I have sent several e-mails but had no responses and despite promises supervisors have never called me back," she said.
The outage has caused problems for customers' businesses that use the e-mail: "Potential customers have not been able to contact me and others have thought we run a bogus business because the e-mail does not currently exist."