The Spam Prevention Early Warning System (SPEWS), whose blacklist is referenced by many antispam controls, imposed the block in response to the high number of Telewest customers whose machines have become compromised and taken over for the purpose of sending spam.
Last month, Silicon.com revealed that some of Telewest's Blueyonder.co.uk home subscribers were sending hundreds of thousands of e-mails each day--a sure sign of an open relay,.
At the time, Matt Peachey, a managing director of, whose Senderbase system revealed the extent of Telewest's spam problem, told Silicon.com: "The ISPs know they're spamming, but they're reluctant to put things in place which block mail. With ISPs, it's not about what comes into their networks; it's about what goes out."
Despite such apparent warnings, a representative for Telewest told Silicon.com the company believes SPEWS' actions have been "a little heavy-handed."
IronPort's Peachey is inclined to agree. "I'm not surprised this has happened, but I am surprised at the number of IP addresses which have been blacklisted," he said.
Peachey said about 17,000 IP addresses on the Blueyonder.co.uk domain are pumping out spam, yet the SPEWS blacklisting applies to more than 900,000.
"This is why blacklists are so problematic," Peachey said. "There will be a lot of people who are blacklisted who have been doing absolutely nothing wrong."
However, Telewest is holding back from any further criticism of SPEWS.
"We have to let them get on with what they do and concentrate on our own game," the representative said. He accepted that Telewest must take some responsibility for the situation reaching such a crisis point but said "it's an industry issue which every ISP suffers."
The Telewest representative said: "We're doing our best to contact customers, and we are talking them through physically cleaning up their PCs."
"Later this year we are launching a very comprehensive security package for our customers including a free firewall, free antispam and free antivirus," he added.
Currently Blueyonder.co.uk is the ninth in the Senderbase list of domains generating e-mail--two places behind Hotmail and two ahead of America Online.
According to Senderbase, Blueyonder.co.uk addresses are generating 90.4 million e-mails per day. The company confirmed it has around 700,000 customers, with updated figures due for release on Thursday.
Will Sturgeon of Silicon.com reported from London.