For a year, Microsoft Corp. has extolled the virtues of the Can-Spam Act, which Congress passed in late 2003 to crack down on purveyors of unwanted bulk e-mail. The company, with other Internet and marketing firms, helped craft the act and has sued several spammers under its provisions.

But Bob Poortinga thinks the software giant is engaged in its own spamming.

Last week, Poortinga got a lengthy "executive letter" from Microsoft chief executive Steven A. Ballmer touting Microsoft's Windows products for companies and other organizations.

The letter was one of a series sent by Microsoft to the technology community as part of a worldwide campaign by Microsoft to combat the growing popularity of the Linux operating system and other open-source software.

Many businesses and government agencies have turned to open-source systems because they consider them to be less expensive, more secure alternatives to Microsoft's Windows software.

"I'm writing to you and other business decision makers and [information technology] professionals today to share some of the data around these key issues, and to provide examples of customers who opted to go with the Windows platform rather than Linux," Ballmer's message said.

Microsoft said Ballmer's e-mail did not violate federal anti-spam regulations. But anti-spam activists and legal experts said the message does not make it easy for people to remove themselves from future mailings, as required by the law.

Like many anti-spam activists, Poortinga, a Bloomington, Ind., programmer, has never been a fan of the Can-Spam Act. He said it is as much an effort to protect corporate marketers' ability to send unwanted e-mail as it is to block unsavory spam.

He said he never gave Microsoft the e-mail address to which Ballmer's note was sent. Poortinga said he primarily used that address to register Internet domains for hosting Web sites.

"It also shows that the Can-Spam Act is simply a worthless exercise in PR and it reinforces the widely held belief that Microsoft is so arrogant that they feel that they are not bound to conform to laws and standards," Poortinga said in an e-mail interview.

Poortinga, who described his experience in a note posted on an Internet discussion group, added that he got an unsolicited e-mail from Microsoft in 1999 and tried to unsubscribe at the time.

As details of his experience and a copy of Ballmer's note were forwarded to other technology mailing lists, some participants speculated that Microsoft was sending its messages to lists containing names other than those in its customer database.

Microsoft spokesman Sean Sundwall said the company "never, ever" uses outside lists for its mailings, although he said he did not know how Poortinga ended up in Microsoft's customer database.

He said that database includes millions of names collected from a variety of sources, including registrations for products or Microsoft-sponsored conferences, names provided to Microsoft representatives at trade shows or requests to receive company newsletters.

He added that Poortinga might not have followed the proper procedure to unsubscribe in 1999, but conceded that the request might have fallen though the cracks.

Sending an unsolicited e-mail once is permitted under the terms of the Can-Spam Act.

That was a sore point with many anti-spam activists, who argued that people should not receive any commercial e-mail unless they specifically request it.

Instead, Congress required bulk mailers to provide for an easy way for people to remove themselves from future mailings. Failure to honor those requests is punishable by fines.

Ballmer's e-mail advised readers that if they wish to receive future letters, they can sign up for them. That way, Sundwall said, if a recipient takes no action he would not get any additional mailings.

The e-mail also included a link to a sign-in page for a Microsoft Passport, which is the system used by the company to verify the identities of its customers.

The e-mail said that by doing so, customers can manage their accounts, such as instructing the company on what type of information they want to receive.

A leading authority on spam laws said Microsoft's approach has several problems.

"The Can-Spam Act requires that there be a clear and conspicuous" notice of how to unsubscribe from future mailings, said David E. Sorkin, an associate professor at the John Marshall law school in Chicago. "It's not clear to me this message even has one."

He said Congress did not intend for people to have to provide additional information to a bulk e-mailer to be removed from a list.

"That seems to me to be a clear violation of the statute," Sorkin said.

Sorkin criticized the section of the message that implies that no further mailing will be sent unless asked for by the recipient. "That's a classic thing found in spam," he said, noting that a bulk mailer could continually make that promise and then keep sending e-mail.

Sundwall said Microsoft's lawyers reviewed the mailings and determined that they complied with the Can-Spam Act.

"Customers who have registered their e-mail address with us always maintain the right to opt out of future e-mails," Sundwall said. "When such action is requested, we immediately remove them from future customer communications."

Chief executive Steven A. Ballmer's mass e-mail promoting Microsoft products has caused a stir among spam opponents.