Guidelines for Names and Titles: The salutation should typically use the person's last name, along with a "Mr." or "Ms." In general, avoid using "Mrs." or "Miss" unless you are certain of how the woman wants to be addressed. When in doubt, default to using "Ms."
In the end, this is all about respect for your recipient. If you’re offering a real solution to a real problem, people want to know about it. By following proper and well_understood formats and keeping your writing clear and engaging, you’re making it easier for them to solve their problem. Provided that you’re honest and have the skills and talents to back up your claims, writing a good, solid letter makes it more likely that both you and your reader will be satisfied. Try it the next time you have to write an important letter.