There are many examples of greetings or salutations used in writing letters. The most common example is "Dear" and to whom the letter is addressed. This salutation is appropriate for most types of letters, whether the writer knows them well, works with them or they are a potential or current employer.
If the writer knows the person well, it is acceptable to address the letter using their first name as in "Dear Fred." If they are an employer or otherwise in a professional setting, the writer should use an honorific followed by their last name, such as "Dear Mr. Hall." They need to make sure to use Mrs. or Ms. for women if the woman is identified as married or not.
Another common salutation is "Dear Sir or Madam." This greeting should be used if one is unsure of the recipient's name. The writer needs to add the appropriate gender title to the salutation.
"To Whom It May Concern" is another common salutation. This should be used in business correspondence if there is not a particular person in mind one is writing to. This kind of salutation is more commonly used when making inquiries. However, every possible effort should be made to find a specific person to write the letter to. Using the correct salutation sets the tone for the rest of the letter and is often the first impression the recipient gets of the sender.