The spam flood is rising, contributing to a reduction in the usefulness of e-mail, a market research firm said Wednesday.

Unsolicited e-mail from con artists, virus writers and advertisers accounts for 38 percent of the 31 billion e-mails sent each day in North America this year, up from 24 percent in 2002, International Data Corp., said in a report on web mail and spam.

In addition, Internet service providers and makers of anti-spam products report that spam represents from 50 percent to 95 percent of all inbound Internet e-mail, IDC said. That's triple the 15 percent to 30 percent levels reported two years ago.

The growing spam avalanche has contributed to a reduction in the usefulness of e-mail. Other factors include the increasing cost of storing and managing e-mail and the growing use of instant messaging.

The number of spam sent on an average day is 11 billion, compared with 4.5 billion in 2002, IDC said. In comparison, the number of person-to-person emails currently sent each day and in 2002 is 12 billion and 10.5 billion, respectively.

Despite these sobering numbers, filtering tools are improving and doing a better job at intercepting spam before it reaches the inboxes of businesses and consumers, IDC analyst Mark Levitt said. Those tools include desktop software, appliances attached to corporate networks and e-mail filtering offered by service providers.

"A year and a half ago, spam was completely out of control and the spammers where having a party at everyone's expense," Levitt said. "That's not the case anymore."

Levitt believes consumers and businesses are controlling the inflow of spam better, based on interviews with information technology executives and individual users.

But while anti-spam efforts appear to be working, consumers, who can't afford the elaborate filtering tools used by companies and remain the most vulnerable to spam, still see it as a huge problem.

The Washington State Attorney General's Office, for example, says spam has been the number one consumer complaint reported over the last two years. The Federal Trade Commission reports receiving more than 130,000 junk email complaints a day, and says the average American gets nearly 2,200 spam messages annually. These messages arrive despite Internet service providers filtering 80 percent to 90 percent of junk e-mail.

Spam, however, is one of three factors dampening the usefulness of email, IDC said. A second factor is the increasing cost for companies of storing and managing e-mail to comply with government and industry regulations and business requirements. Adding to the cost is the volume of business e-mail, which increased by 47 percent this year from 2003, and doubled from 2002 levels.

As a result, corporations are searching for alternatives to reduce the use of e-mail or for technology and policies that make it more efficient, IDC said.

The third challenge to e-mail is instant messaging, which has punctured e-mail's monopoly on text messaging. Consumers have not only embraced IM, but employees in many businesses are also taking advantage of its immediacy and ability to identify whether a worker is available to receive a message.