(FORTUNE Magazine) – A president under impeachment; a new technology containing damning evidence; a frantic last-minute appeal. Yep, 1868 was a remarkable year. As Alan Westin, Columbia professor and publisher of Privacy and American Business, points out, Andrew Johnson's backers unsuccessfully fought to keep telegraph records away from the congressional panel seeking to unseat him. Long before Monica's E-musings on presidential privilege were sampled by Ken Starr, the battle to keep high-tech communications private had been fiercely contested--and usually lost, since courts have tended to rule that new technologies don't deserve special protection. As both Lewinsky and Bill Gates could tell you, it's best not to E-mail anything you don't want to read on the front page of the New York Times.

With Gates' E-mail at the center of the Microsoft antitrust trial, businesses are learning that their electronic communications can be used against them in court. Jim Browning, who studies the E-mail industry for the Gartner Group, a research firm based in Stamford, Conn., says that the Microsoft case has a lot of his clients in a swivet. "Every time a high-profile case like this comes along, we get more inquiries," he says.

The problem lies in the fact that just like paper memos past, E-mail creates legally binding documents. But E-mail is a plaintiffs lawyer's dream, since, unlike paper memos, it's hard to destroy. Even if both the sender and recipient delete a message, it can reside in the company's computer system, just waiting for a data specialist to retrieve it. John Jessen, CEO of Electronic Evidence Discovery in Seattle, hunts for antique computers that can read obsolete file formats. "We buy old computers from secondhand stores, we buy them from Goodwill," he says. "We even found a guy who had every computer Radio Shack ever made up in his attic. Luckily for us, his wife was pushing him to get rid of them."

Another advantage over paper memoranda: Rifling through electronic documents is as easy as hitting "find." "The great thing about E-mail is that you can use a keyword to look through it," explains Jim Bruce, a Washington, D.C., attorney who advises the Electronic Messaging Association. "In the old days, when you subpoenaed records, opposing counsel would back up a loaded semi and say, 'It's all yours! Have fun!'"

E-mail is unlikely to disappear from the courts, so experts like Browning and Bruce advise clients to establish a clear E-mail policy: Archive messages methodically if they're critical business records; expunge them quickly if they're not; and make clear to employees that the E-mail system belongs to the company, not to them.

--Eryn Brown