Yesmail's settlement with the Federal Trade Commission last week sent tremors throughout the industry as other e-mailers scrambled to figure out how the company became ensnared in the FTC's spam-fighting apparatus and how they could avoid a similar scenario.

Yesmail agreed to pay $50,717 to settle charges that its recently acquired @Once unit violated the Can-Spam Act.

The alleged violations happened in 2004. Yesmail acquired @Once in 2005.

Though the size of the settlement was relatively small, the FTC's press release and complaint were worded such that it was difficult to tell what happened and whether or not others are in danger of coming into the FTC's crosshairs under similar circumstances.

According to the FTC, @Once's spam-filtering software blocked some "reply to" unsubscribe requests from recipients as spam, resulting in @Once failing to honor those opt-out requests and sending thousands of e-mails to recipients more than 10 days after the requests, a violation of the Can-Spam Act.

The announcement raised eyebrows in the industry because it looked as if @Once was the victim of a technical glitch. The Can-Spam Act contains a provision protecting senders whose opt-out mechanism "is unexpectedly and temporarily unable to receive messages or process requests due to a technical problem beyond the control of the sender if the problem is corrected within a reasonable period of time."

Lisa Hone, assistant director, division of marketing practices for the FTC, said @Once's glitch failed to meet the requirements of the Can-Spam Act's safe harbor provision, but declined to say why.

A source close to Yesmail, however, said @Once's run-in with the FTC resulted from failing to recognize and fix the problem quickly enough.

"They said it went on too long," said the source, who asked not to be identified.

Unfortunately for Yesmail, at least one of the e-mail addresses @Once failed to remove from its files was one the FTC was monitoring, the source said.

Also, contrary to the FTC's assertions that @Once's spam filters tripped it up, @Once's FTC troubles resulted from the company's bounce-processing and reply-handling technology misclassifying some "reply to" opt-outs as soft bounces, or messages stating that the e-mail couldn't be delivered to the address for a temporary reason.

It took between three and four months for @Once executives to realize that some "reply to" opt-out requests weren't being processed, the source said. The main reason it took so long to recognize the problem was that the mishandled requests were a minuscule percentage of the company's volume -- something like 1,200 messages among a total of 5 million to 10 million bounces and unsubscribe requests, the source said.

FTC officials and Yesmail executives never met face-to-face to discuss the matter, but Yesmail decided to settle because disputing the issue would be more hassle than it was worth, the source said.

And yes, the same thing could happen to anyone in the industry, the source added.

"What it means is you've really got to have good audit controls," the source said. "A privacy officer isn't enough; you need an audit compliance person."