Alibris, an online rare-book seller, pleaded guilty to intercepting e-mail between its clients and online retail giant Amazon.com, the U.S. Attorney's Office in Boston said today.

Alibris agreed to pay $250,000 to settle criminal claims by U.S. Attorney Donald Stern that it intercepted e-mail messages to its clients from Amazon.com. Alibris, of Emeryville, Calif., said it no longer offers clients e-mail service, but its corporate predecessor, Interloc Inc., did.

Stern's office contends that Interloc intercepted the messages between its customers and Amazon.com in part to gain commercial advantage by gathering information on its customers' purchases and obtaining market data.

Alibris admits to the wrongdoing but said it gained no commercial advantage because it already knew what its customers were buying.

Rather, according to president and chief executive Martin Manley, the company broke the law when it tried to rectify complaints from some clients who said they weren't receiving e-mail messages from Amazon.com. In tracking such messages to determine the problem, the company unlawfully captured the messages, although Manley said it did not read them.

"The conclusions reached by the government in this, with respect to motive, are not necessarily ones we share," Manley told Reuters.

Assistant U.S. Attorney Jeanne Kempthorne, who is prosecuting the case, said there is no evidence anyone suffered financial harm as a result of the conduct, which occurred in 1998 and involved nearly 4,000 electronic messages.

But, she added, "I think the violation of privacy is a material harm."