Demon Internet has blamed its own customers for the poor network services over the past week.
The internet service provider (ISP) said that a large number of open relay mail servers vomiting out unsolicited mail was the root cause of the problems.
Deborah Rodger, head of communications at Thus, which owns Demon, said that the problems which dogged the network over the last seven or eight days were "due to the impact of unsolicited mail on the network".
She explained that a large number of end users, which presumably host their websites with Demon, had misconfigured mail servers.
Such misconfigured servers can act as an open relay, which is a favourite of spammers who can hijack them and send unsolicited mail that can't be traced back.
Rodger said that the quantity of unsolicited mail had affected the performance of the mail services in recent days.
She added that Demon is in the process of "shutting down the offending customers and helping them reconfigure their systems".
Rodger confirmed that none of the misconfigurations were thought to be deliberate and that it was spammers from outside Demon's customer base that were misusing the mail servers.
The ISP's status report for today says: "The difficulties customers are experiencing with sending mails are ongoing. Our engineers continue working to minimise the impact of this issue."
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