Mining employee e-mails is "something the company has an interest in, and we are starting to see that interest grow," says Carl Jones, director of collaboration services at The Boeing Co. in Chicago. He says the company has a knowledge management pilot project that, among other things, examines e-mail messages.

"If you have a business problem, you may be able to mine across the e-mail spectrum and find out, hey, there are people out in the field who are subject- matter experts that can help you," says Jones. But, he adds, "we'll have to be very careful about policies on privacy and so on."

Jon Kleinberg, a professor of computer science at Cornell University , says much can be learned from the networks created by people's activities on the Internet.

"How can you infer that someone is influential?" he says. "Is it the obvious things, like they send and receive the most messages, or is it more subtle things, like they operate at the periphery [of a group] but pull together groups that are otherwise weakly connected?"

Kleinberg says answers to such questions may have profound importance for companies that sell online and rely on word-of-mouth recommendations via customers' e-mail. He's looking into two competing theories as to why that kind of e-mail sometimes leads to snowballing sales and other times fizzles.