When you're writing formal letters or e-mails, the most common way to start them off is with:

• the word "Dear"
• the title of the person who you're writing to ("Mr." or "Ms.")
• the person's last name
• a comma (",") for less formal letters or a colon (":") for more formal ones

For example:

Dear Ms. Yokoyama:

Dear Mr. Traven,

But you shouldn't address all letters and e-mails this way. Most personal messages just begin with "Hi (first name),". But you should use the more formal greeting above in these situations:

• You're writing to a customer who you don't personally know.
• Your message might involve some legal action.
• You're applying for something like a job or admission to a school.