"She must not swing her arms as though they were dangling ropes; she must not switch herself this way and that; she must not shout; and she must not, while wearing her bridal veil, smoke a cigarette." – Emily Post (Etiquette in Society, in Business, in Politics, and at Home, 1922)

When we think of etiquette, we often think of those traditional dos and don’ts our mothers taught us. Don’t put your elbows on the table. Don’t talk with your mouth full. Always send a thank-you card. But as Ms. Post and 21st century etiquette authority Jacqueline Whitmore would tell you, etiquette is not just about avoiding faux pas with the finger bowl. It’s all about the way you treat people—even at work.

“I call it the Platinum Rule,” says Whitmore, founder of The Protocol School of Palm Beach and author of Business Class: Etiquette Essentials for Success at Work. “Treat others the way you would like to be treated. It summarizes what business etiquette is all about. It’s not necessarily the way you use your knife and fork, although that’s important. Making other people feel comfortable is what’s most important.”

But just how does a bizgal uphold any “ladylike” virtues when the rest of the workplace is increasingly competitive, casual, and ungraciously gadgetized? In this frenzied world of business on the fly and 24/7 texting, do manners even matter any more?

According to Whitmore, YES. “Manners are part of your personal brand,” she explains. “If I said to you, ‘Who was the nicest girl you ever went to school with?’ you could probably come up with a name. Well, that nicety or niceness was part of that person’s brand.”

Think of it this way: if you went out on a blind date and the guy ordered you a salad, checked the scores on ESPN while you were speaking, and picked spinach out of his teeth with a steak knife, would you go out with him again? That’s a no. And impressions work the same way in the realm of business.

“If your manners are good, you’ll be judged favorably by others, and if your manners are poor, you’ll be judged less favorably,” says Whitmore. “Manners affect the way other people relate to you and think of you and treat you.”

How so? Whether right or wrong, bosses will promote and clients will do business with...the people they like. And no, this isn’t any modern revelation. Dale Carnegie wrote How to Win Friends and Influence People, perhaps the most famous self-help book on success, all the way back in the 1930’s. But his principles of being genuinely interested in other people, being a good listener, remembering someone’s name, smiling—all of these character strengths are still very valid points of occupational politeness today.

It’s just wow, the world and the workplace have changed. In 2008, women comprised 46.5% of the total U.S. labor force (compared to 30% in 1950). There are now three, possibly four different generations of employees trying to eke a living in the same job market. And, last but not least, email and smart phone technologies have made it a whole lot easier to communicate and multi-task, and just as easy to be rude. (Can you hear me now?)

These are all dynamics that make the “do’s and don’ts” of business etiquette a bit more difficult to navigate these days. And according to Whitmore, some of the most important professional courtesies are the things “they never teach you in school or tell you about at work.”

You might call them “the unwritten rules of the office,” and you might want to brush up. Turns out minding your manners can get you a lot of things: a sale, a promotion, respect from your peers, the award for Ms. Congeniality—and at the very least, approval from your very own mother.

For more information on Jacqueline Whitmore’s book and business etiquette webinar series, check out www.etiquetteexpert.com.