Being too casual
While the tone of your message should reflect your relationship with the recipient, Haefner says, too much informality will make you come across as unprofessional.
She advises being judicious in your use of exclamation points, emoticons, colored text, fancy fonts, and SMS shorthand.
What's more, not everyone can quickly decode acronyms, Rosalinda Oropeza Randall, an etiquette and civility expert and the author of "Don't Burp in the Boardroom," tells Business Insider.
"Be especially mindful if you work with people from different generations, have language barriers, or prefer a more traditional tone," she says.