The Spamhaus Project has told a US court that it plans to appeal a recent ruling that threatened the volunteer organization with millions of dollars in legal fines and a possible shutdown of database of known spammers.

The notice was filed Friday in the US District Court for the Northern District of Illinois by lawyers with Jenner & Block, a Chicago law firm that is now representing Spamhaus.

Spamhaus, based in the UK, has a team of 25 investigators and claims to block between eight billion and ten billion email messages per day. Its database is used by several major security vendors, including Microsoft.

The filing marks the group's return to a legal fight against an email marketing company called e360 Insight that Spamhaus had tried its best to ignore.

Spamhaus had not shown up in court to dispute the charges against it, and the organisation has made it clear that it does not accept US jurisdiction over its activities. However, this position was apparently reconsidered after a proposed court order was published earlier this month calling on the Internet Corporation for Assigned Names and Numbers (ICANN) and Spamhaus's registrar, Tucows, to pull the project's domain name.

"Spamhaus is concerned at how far a US court will go before asking itself if it has jurisdiction, and is intending to contest the ruling in order to stamp out further attempts by spammers to abuse the court system in this way," the organisation said in a statement on its website.

The order, written by the plaintiffs in the case, does not have the force of law, but if the judge decides to accept it, observers said that it could kick off a power struggle between ICANN, which is responsible for the internet's domain name system, and the US courts.

Spamhaus's new legal counsel, Jenner & Block, is a well-respected firm with over 400 lawyers.

It has offered its services in the case for free, said John Reid, a Spamhaus volunteer. "We are a nonprofit organisation; spammers know this. That's why they sue, hoping we cannot afford to defend ourselves," Reid said. "Luckily, since we're the good guys, there are a lot of great lawyers, law firms, and law professors around the world willing to step up and help."

"We were asked to provide support by a number of folks with whom we've been associated in the past," said Matthew Neumeier, a partner with Jenner & Block. He declined to say who had asked the firm to help out in the case.

E360 Insight could not be reached immediately for comment on this story. In a statement on its site, the email marketer cited Spamhaus's earlier decision to walk away from the case as evidence that it "could not produce its justification for the listing of e360 on its blacklists".