"CC" is fast becoming the most dangerous letter combination in the business world.

Scott Stratten recalls the day the president of his company e-mailed 70 employees about a planned meeting. They all began giving him their comments using the "reply to all" button. As the e-mails flew, cc'd to everyone, a vice president asked the president: "How's the prostate?"

The president ended up calling a meeting to reassure employees that his prostate was fine. But from then on, some privately referred to him as "President Prostate."

As e-mail overload buries computer users world-wide, much of the blame is falling on the cc line, which allows e-mailers to share correspondence with countless colleagues, friends or strangers. For e-mail writers who play office politics, deciding which recipients belong on which lines -- "to," "cc," or "bcc" (blind carbon copy) -- has become a daily struggle. Many resort to unnecessary cc-ing and sneaky bcc-ing, inadvertently spilling proprietary information, or inappropriately copying an underling or boss.

The "cc" gridlock isn't just impeding worker productivity. It's also increasing management's legal risks, according to a study set for release this week. As a result, Internet consultants are advising companies to develop e-mail rulebooks, and recommending new technological tools, such as the color-coding of less-vital cc'd messages.

Ivan O'Sullivan knows the business risks of an errant cc. A few years ago, as vice president of a Massachusetts-based Internet firm, he was working on a $5 million bid for another company. Then his boss wrote a secret e-mail detailing his negotiating strategies. On the cc line, the boss meant to include an underling named John, but absentmindedly cc'd an officer named John at the target company. The deal collapsed. Mr. O'Sullivan is now a vice president at Clearswift, a software firm that offers technology to make sure confidential e-mails can't be cc'd inappropriately. The cost: about $30,000 for a company with 1,000 employees.

Such high-tech solutions are helpful, but many "cc" problems could be solved with some common sense and discretion. The first step is to understand key distinctions. The "to" line is for someone who needs to directly respond to an e-mail. The cc line is an "fyi" courtesy; usually, cc recipients needn't feel obliged to reply.

Some people get territorial about which line they're on -- "to" or "cc" -- considering it a sign of their importance to a project. With such associates, it's best to ask if they have a preference.

In interoffice correspondence, the bcc line, often called "the evil brother of cc," should be used sparingly -- only when it's crucial to go behind someone's back.

With so many employees abusing the cc line, some firms are beginning to formalize these rules. The Steak Escape restaurant franchise chain has banned bcc's, and instructs only senders and recipients to archive their e-mails. If employees are copied on e-mails, they're told to delete them eventually.

But at the majority of companies, there's a cc culture run amok. Last year, Mr. Stratten, a corporate trainer in Toronto, worked at a manufacturing firm where employees seemed addicted to trading "reply to all" e-mails. "Every comment, every 'I agree,' every 'uh-huh' was sent to every staff member," he says. "You'd get 35 messages, and most were just virtual nods of the head."

Employees seem most addicted to nodding at the boss. That's why it's crucial to check your supervisor's cc tolerance level by asking: How much e-mail do you want to see?

Middle managers haggling with other middle managers on a project should resist cc-ing the big boss on e-mail exchanges. "It's like running to the teacher," says Mr. O'Sullivan.

In a new study of e-mail usage in North America, more than half of respondents cite the "cc" and the "reply to all" functions as their chief pet peeve, says Christina Cavanagh, the University of Western Ontario management communication professor who led the research project.

Meanwhile, the rampant use of cc and bcc to discuss sensitive corporate issues is making it easier for regulators and attorneys to round up smoking-gun e-mails. In the survey being released this week by the American Management Association, the ePolicy Institute and Clearswift, 14% of respondents at 1,100 U.S. companies said they've been ordered by a court or regulator to produce employee e-mail, up from 9% in 2001.

Among the solutions offered by experts:

  • Create rules: The ePolicy Institute's Nancy Flynn advises companies to follow her three "E's" of e-mail management: Establish written e-mail policies. Educate the work force about e-mail risk. Enforce rules with software. "Courts look favorably upon employers who demonstrate that they have a policy and have educated their employees," says Ms. Flynn.

  • Know your computer's capabilities: Some e-mail systems, such as Microsoft Outlook, let you identify less-urgent e-mails by color. You can also direct cc's to a subfolder in your inbox.

  • Hide sensitive e-mail addresses: That's when the bcc option makes sense. Among the sort of mistakes you'll avoid: During Robert Reich's 2002 campaign for governor of Massachusetts, his staff put hundreds of subscribers on its e-newsletter's cc line, which allowed the competition (and spammers) to harvest their e-mail addresses.

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