In just over a decade since its mainstream debut, e-mail has become one of the most important communication tools for businesses everywhere, if not the most important communication tool.

In fact, the number of person-to-person worldwide e-mail messages sent on an average day in 2005 was 33.3 billion or about 8.8 trillion annually, according to IDC, the Framingham, Mass. research firm. “Person-to-person” means these numbers do not include spammed messages or any other automated e-mails.

Think you know all there is to e-mail etiquette? Think again.

With so much virtual communication going on, here’s how to avoid the pitfalls:

To, Cc and Bcc

Many business e-mail users still make the mistake of including all recipients in the “To” or “Cc” fields. Not only may that upset those who want to keep their e-mail address private, but you’re showing your naiveté about three basic rules.

  • The “To” field should be reserved for writing an e-mail to one person.
  •  “Cc” stands for “carbon copy” and can be used when you want to include others and it’s okay for the recipient to see the others’ e-mail addresses.
  • A “Bcc,” on the other hand, which stands for “blind carbon copy,” is when you don’t want the recipient to see you’ve also sent the same message to others -- or when you don’t want all the recipients to see each other’s e-mail address for privacy reasons.

“Employees who use the ‘To’ field instead of the ‘Bcc’ field aren't properly trained by their employer or they don't realize the risk of e-mail viruses picking up all those addresses in the ‘To’ field,” says Andy Wibbels, a computer expert and author who has worked with hundreds of small businesses. “System administrators should also consider flagging e-mails where people put a ton of folks in the ‘To’ field.”

Be cautious when clicking “Reply to All” when only the original sender needs to read your reply. You don’t know if the sender has added Bccs and it’s amazing how many business people divulge sensitive information about products, customers and/or employees to unintended recipients this way.

Keep it simple

Brevity and directness are the key to business correspondence. That includes e-mail. With more than 100 e-mails in a typical inbox a day, no one wants to read a novel. Keep it simple. And this applies whether you’re the boss or the lowest rung on the corporate ladder. “E-mails should be under two paragraphs with formatting and bullets to illustrate key points and needed actions,” advises Wibbels.

Be sure what you’re communicating is clear and near the top as our attention span tends to drift as our eyes scan down the page. ”If you can make your point in the subject line, all the better,” Wibbels says.

Be a pro

Writing e-mail to colleagues, clients, and coworkers needs to be professional. Don’t gossip about someone in the office. Don’t add five exclamation marks at the end of a sentence. Spell check. Go easy on the emoticons (e.g. ;-) ).

“E-mails with subject lines of 'Hey!' or 'OMG!' or 'Re: re: re: fwd: this.' only annoy and waste time,” adds Wibbels. “And clean up e-mails when you forward them [as] nobody likes reading all the e-mail header junk and all the indenting over and over again.”

When to send and e-mail

Don’t write an e-mail when you’re upset or angry at someone (or at least don’t click “Send” until you’ve read it with a leveled head). Remember, you must be professional at all times. Anything you write and send can live forever and may come back to haunt you, maybe even in court.

Big Brother could be watching

If you’re not the boss, your e-mail and other Internet behavior may be monitored by your employer. Preston Gralla, author of How the Internet Works, says software, such as a keystroke loggers “can record every word of every document created on the computer.” Gralla says an estimated 36 percent of employers track the content employees view as well as monitor their keystrokes and time spent at the keyboard.

Attachments & threads

While most of your e-mail correspondence with someone will likely be via a broadband connection, don’t attach a 10MB PowerPoint presentation. These days, they may be picking up e-mail via a cell phone or BlackBerry. Wibbels says that if you’re e-mailing inside your company, use an intranet network drive for file transfer instead. You might want to ask permission first before sending a large file to someone outside the firm. You can also use an online delivery service, such as YouSendIt.com, which allows the recipient to click a Web link to download the file outside of their e-mail program.