What three words have a total of only 14 letters yet carry a great deal of meaning? People may not notice these words when they're there, but if you forget to use them, you'll come across looking disrespectful and ungrateful. Give Up? These very powerful words are "Please" and "Thank You." Please take my advice. You'll thank me later.
Many people are offended if strangers address them by their first names. When in doubt, use Mr., Mrs., or Dr. (if appropriate). When you are replying to an email and the sender of the original message has used his or her first name only, then you could safely assume it's okay to use that person's first name as well.