lyx Sachs is no longer sending people e-mail offering to "fix your credit risk free."

Confronted by an increasing number of individuals, businesses and Internet service providers using software meant to identify and discard unwanted junk e-mail — commonly known as spam — Ms. Sachs has been forced to become more creative in her marketing pitches. The subject line on her credit e-mail, for example, now reads "get a fresh start."

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From a small office on Sunset Boulevard in Los Angeles, millions of messages prepared on behalf of others by Ms. Sachs and her partner are still going out to e-mail in-boxes every day, promising not just to restore a poor credit rating but also to sell printer ink, 3-D glasses and, lately, even playing cards with pictures of wanted Iraqi leaders.

In the cat-and-mouse game of e-mail marketers and those trying to stop them, the spammers are still winning.

So far, nothing that has been tried to block spam has done much more than inconvenience mass e-mailers. Just as Ms. Sachs's company, NetGlobalMarketing, has been able to reword its e-mail to evade spam filters, others use even more aggressive tricks to disguise the content of their messages and to send them via circuitous paths so their true origin cannot be determined.

"There is no silver bullet," said Lisa Pollock, the senior director of messaging at Yahoo, the popular Web portal. "There will always be people who can find a way to get around whatever you have in place."

No doubt making a living selling things by e-mail is becoming harder. Not only are more messages being blocked by automated antispam systems, more senders of e-mail are also facing legal action. Last week, America Online and the Federal Trade Commission each filed suit against e-mailers that they say are illict spammers. Congress is seriously considering legislation to crack down on spam.

But the infestation is growing faster than the antispammers can keep up. Brightmail, which makes spam-filtering software for corporate networks and big Internet providers, says that 45 percent of the e-mail it now sees is junk, up from 16 percent in January 2002. America Online says the amount of spam aimed at its 35 million customers has doubled since the beginning of this year and now approaches two billion messages a day, more than 70 percent of the total its users receive.

Indeed, the spam problem defies ready solution. The Internet e-mail system, designed to be flexible and open, is fundamentally so trusting of participants that it is easy to hide where an e-mail message is coming from and even what it is about.

Another reason there is so much spam is that, with a simple computer hookup and a mailing list, it is remarkably easy and inexpensive to start a career in e-mail marketing. Companies that offer products like vitamins and home mortgages as well as those selling items like penis and breast enlargement kits will allow nearly any e-mail marketer to pitch their wares, paying a commission for any completed transaction.

The microscopic cost of sending e-mail, compared with the price of postal mailings, allows senders to make money on products bought by as little as one recipient for every 100,000 e-mail messages. Internet marketing companies typically charge $500 to $2,000 to send a solicitation to a million in-boxes, but the cost goes up if the list is from a reputable source or is focused on people in certain favored demographic groups. Sending the same offer to a million people by mail costs at least $40,000 for a list, $190,000 for bulk-rate postage and more for paper and printing.

Albert Ahdoot, for example, started a part-time business using e-mail to sell printer-ink refill systems while he was in college. When he dropped out of medical school, he hooked up with Ms. Sachs, a former producer with Geraldo Rivera who later worked in marketing at several Internet companies. With her client contacts, his technology and some e-mail lists they acquired, they started their business about a year ago.

Like many in the e-mail marketing business, Ms. Sachs says her e-mail blitzes are not spam because she sends them only to lists of people who have agreed to receive marketing offers over the Internet. These opt-in lists, as they are called, are generated when Internet users enter a contest on the Web or sign up for an e-mail list in which the fine print says the user agrees to receive "occasional offers of products you might find valuable from our marketing partners."

Arguing that no one is forced to sign up for e-mail pitches, Internet marketers say that the attack on spam has already gone too far, interfering with legitimate business.