People treat email very casually, says corporate trainer Paula Goebel, but in the workplace, “Your credibility, professionalism and competence will be judged based on how you communicate online.” Be perceived as a professional by following these tips from Goebel.

1. Be concise. Longer messages are difficult to read, and most people will put them aside.
2. Avoid sarcasm and too much humour. It can come across as rude or abrupt because the recipient can’t gauge your body language.
3. Use a descriptive subject line that’s no more than four to five words. Avoid important and urgent.
4. Don’t send an email when emotional or angry. Sit on it for 24 hours.
5. Avoid emoticons or textese. This should be reserved for personal email.
6. Remember, email is not private. Don’t put anything in email that you wouldn’t “want the whole world to know about.”
7. Think twice before hitting reply all. Ask yourself, “Do all these other people really need to hear my reply?” If not, reply only to the original writer.
8. Don’t send a thank-you email in reply to a thank-you email. ”What I find is people are thanking someone for a thank you, and it just doesn’t make sense.”
9. Proofread, proofread, proofread. Check for spelling, typos and word usage.
10. Respond within 24 hours. If you require more time, let the sender know you’re reviewing the email and when you’ll get back to that person.
11. Never use all caps or all lowercase.
12. Start withhi, hello, good afternoon or good morning. Avoid dear; it’s too formal.
13. The proper closing would be thanks or regards. Sign your full name when emailing clients; your first name is fine with colleagues. After multiple email exchanges initials are fine.
14. The ideal font is Arial.
15. The ideal font size is 12.

Source: http://www.techlifemag.ca/875.htm