In the last year, spam has grown from a nuisance to a nightmare for corporate network executives, who are scrambling to respond to the increased volume and objectionable content of unsolicited commercial e-mail messages sent to end users.

In response, messaging vendors are beefing up their antispam filtering capabilities targeted at corporate customers. Among the vendors that started shipping new antispam offerings in recent weeks are Lotus, Mirapoint, Sendmail and Tumbleweed.

Meanwhile, Brightmail, a big player in antispam packages for the service provider market, in October stepped up its push into the enterprise market with Version 4.0 of its Anti-Spam software. Brightmail's enterprise customers include Cypress Semiconductor, Motorola and Lycos.

All these companies sell software designed to identify and stop spam at the edge of corporate networks, before these unwanted messages arrive at corporate e-mail servers or are sent to end users. At the same time, these software packages aim to maintain e-mail system performance and reject as few mission-critical e-mail messages as possible.

"Enterprises are concerned about protecting their networks at the perimeter, at the e-mail gateway," says James Kobielus, a senior analyst with Burton Group, which in November issued a report on combating spam, and a Network World columnist. "They want a floodwall essentially to catch spam . . . [before] spam becomes a huge consumer of resources, including bandwidth, CPU and mail administration."

The sheer volume of spam is what's driving more corporations to purchase antispam filtering software. Spam represented between 8% and 10% of all e-mail messages on the Internet a year ago, but it has grown to as much as 30% to 40% of the messages corporate users receive today, experts say.

"Spam is the No.1 problem facing e-mail administrators and e-mail users," Kobielus says. "It's out of control. . . . And the problem has gotten significantly worse in the last year. The volume has grown by a multiple of four to five in a year."

Pornographic spam, in particular, is on the rise. Kobielus says it has doubled in the last year and now accounts for 10% of all spam.

Network managers are tackling the spam problem because of the potential legal liability associated with pornographic spam and concerns about the negative effects on end-user productivity. High volumes of spam are a drain on network resources such as e-mail server capacity, Internet bandwidth and e-mail archives.