Demon Internet suffered a significant outage on Wednesday, triggered by a catalogue of disasters which sent problems rippling through the rest of its network.
Problems started early on Wednesday morning when the electricity supply feeding the service provider's Network Operations Centre in Finchley failed.
The back-up generator kicked in but then itself suffered a fault which required the replacement of specialist parts, the firm said.
Standby batteries for the back-up were exhausted by the time the repairs were completed, knocking out Demon's email and e-commerce services. Some leased line users lost their connection completely.
Customer service phone lines also suffered, leaving users with a restricted service as they tried to discover what was going on.
Power was restored on Wednesday evening but the backlog of traffic on the servers is still clearing, with email services bearing the brunt of the problems.
Users who contacted vnunet.com said that Pop3 email access is still down, and some are still waiting to receive mail from yesterday morning.
A spokeswoman for Demon explained that, although customers did not receive email for part of yesterday, "no mail was lost, and all messages were stored and passed through as soon as was possible".
Engineers are still working to get the load on the servers back down to a manageable level.
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