By Maggie Shiels in San Francisco

A US law firm has become the hero of the common people for its decision to take on the spam merchants who wage guerrilla warfare on our e-mail inboxes, offering everything from sex to cars and easy money to psychic readings.

The San Francisco office of Morrison and Foerster, also known as MoFo, is one of the first outfits in the United States to take on spammers who send out unsolicited commercial e-mail.

For six months the company logged at least 6,500 spams which were sent to its staff on a daily basis.

One click could cost $50

Michael Jacobs, who is a partner at MoFo and chairs its technology committee, says e-mail is "mission-critical" to his firm.

"We live on e-mail. We use it to communicate with our clients. We use it for internal communications. We are trying to work very quickly and efficiently and spam was degrading our ability to do that."

In its fight, MoFo is suing a Silicon Valley e-mail marketing firm called Etracks. Mr Jacobs says while it wasn't the only company sending unsolicited commercial e-mail (UCE), it was one of the biggest offenders and more importantly it's based in California.

Damages claim

In the US there is no blanket federal law governing junk e-mail and the 20 states which have introduced their own laws can only enforce them within their borders. No one has been prosecuted under California's four-year-old statute.

Take these jerks for everything they've got - I love you

An admiring e-mailer

In its suit, MoFo says Etracks broke California's anti-spam laws by sending unwanted e-mail and advertising a range of items without the required advertising label and using the company's mail server to distribute the e-mails.

MoFo also claims a legally mandated free phone number or valid return e-mail service to request removal from the marketer's list was missing.

The suit, filed in San Francisco's Superior Court, asks for damages of $50 (£35) for each e-mail received with a maximum daily amount of $25,000, the limit set by law.

Preference service

The lawyers for Etracks did not return calls to BBC News Online but its attorney Kenneth Wilson told the San Francisco Chronicle that Etracks only uses e-mail lists provided by clients who assert the recipients have opted to receive its messages or have an existing relationship.

On its website Etracks says it is a member of the Direct Marketing Association, an 85-year-old organisation which sets out ethical guidelines to its 5,000 members on best practice.

The organisation distances itself from spamming.

"No DMA member can send spam and the DMA agrees that people should be able to ask to get off mailing lists and stay off," says DMA's vice president of ethics and consumer affairs, Pat Faley.

Reading and clearing e-mails takes time

To that end the DMA has designed the "e-mail preference service" where anyone can submit their e-mail address to be removed from all members' lists, says Ms Faley.

The problem, she says, is that it has no control over anyone who is not a member of DMA.

While Etracks clearly carries the DMA logo on its website, Ms Faley says there's no record of the company's membership either past or present. The matter has been referred to its legal department.

State law

The Coalition Against Unsolicited Commercial E-mail, or CAUCE, says this case highlights the need for a national approach to a problem that is seriously undermining business.

There are enough stresses at work without junk mail

Spokesman Ray Everett-Church, who helped draft California's anti-spam laws, says e-mail is a "critical part of the world economy today".

"If you cause people to think twice about engaging in some business transaction over e-mail for fear it will cause more spam you are putting a damper on the growth of what is an incredible global commerce and communications medium."

A 2001 survey by the European Commission estimates that spam costs consumers an estimated $8.8bn a year worldwide just in connection costs.

Internet research company Jupiter Media Metrix predicts consumers will receive about 206 billion junk e-mailings by 2006 - an average of 1,400 per person. Each piece of spam is said to cost $1 in lost productivity.

Ray Everett-Church: "E-mail critical to economy"

At MoFo, the suit has received unprecedented public backing. The level of sentiment expressed in one e-mail is indicative of the kinds of messages it has been getting.

It reads: "I hate spam as much as the next guy. Take these jerks for everything they've got. You are pinch hitting for all of us. I love you."

Mr Jacobs says it's unusual for a law firm to be loved by the public and it's great.

"I have been practising for over 15 years and I have never done anything as a lawyer that has been this popular."