1. Include a clear, direct subject line.

Examples of a good subject line include "Meeting date changed," "Quick question about your presentation," or "Suggestions for the proposal."

"People often decide whether to open an email based on the subject line," Pachter says. "Choose one that lets readers know you are addressing their concerns or business issues."

2. Use a professional email address.

If you work for a company, you should use your company email address. But if you use a personal email account -- whether you are self-employed or just like using it occasionally for work-related correspondences -- you should be careful when choosing that address, Pachter says.

You should always have an email address that conveys your name so that the recipient knows exactly who is sending the email. Never use email addresses (perhaps remnants of your grade-school days) that are not appropriate for use in the workplace, such as "babygirl@..." or "beerlover@..." -- no matter how much you love a cold brew.

3. Think twice before hitting 'reply all.'

No one wants to read emails from 20 people that have nothing to do with them. Ignoring the emails can be difficult, with many people getting notifications of new messages on their smartphones or distracting pop-up messages on their computer screens. Refrain from hitting "reply all" unless you really think everyone on the list needs to receive the email, Pachter says.

4. Use professional salutations.

Don't use laid-back, colloquial expressions like, "Hey you guys," "Yo," or "Hi folks."

"The relaxed nature of our writings should not affect the salutation in an email," she says. "Hey is a very informal salutation and generally it should not be used in the workplace. And Yo is not okay either. Use Hi or Hello instead."

She also advises against shortening anyone's name. Say "Hi Michael," unless you're certain he prefers to be called "Mike."

5. Reply to your emails -- even if the email wasn't intended for you.

It's difficult to reply to every email message ever sent to you, but you should try to, Pachter says. This includes when the email was accidentally sent to you, especially if the sender is expecting a reply. A reply isn't necessary but serves as good email etiquette, especially if this person works in the same company or industry as you.

Here's an example reply: "I know you're very busy, but I don't think you meant to send this email to me. And I wanted to let you know so you can send it to the correct person."