UUNet blamed an attempt by a Canadian firm to send commercial junk e-mails on a massive scale for the failure which provoked a storm of complaints from businesses.
More than two million spam e-mails swamped UUNet last Thursday, bringing its mail servers to a halt until Monday morning and disrupting e-mail services to one million dial-up users.
UUnet said that it could take up to 72 hours to clear the backlog of e-mail traffic and warned customers who called to complain not to expect normal service for another week.
“Although most of the e-mails have now been deleted, the quantity of genuine mail stored is so great that the system, which serves around million users, is continuing to pass mail only slowly,” the company said in a statement.
The failure has provoked complaints from small businesses using UUNet’s Pipex service which fear that they may have lost valuable business.
Greg Pos, who runs a small business selling stamps and books on Web auction site E-bay, said the failure could lead to his company being de-listed from the E-bay site.
“I could be literally struck off E-bay if I get a negative response from the customers I have not been able to contact,” he said.
On Monday, UUNet staff told Pos that the problem had been caused by building contractors severing a UUNet cable, contradicting official company statements - but this was later denied by a UUNet spokesman.
UUNet was hit by a 36-hour outage in October last year, when 400 customers, including Ford and the London Stock Exchange, were denied Internet access following a major upgrade. At the time, users sought reassurances from UUNet that the outage would not be repeated.