As mentioned previously, application letters and cover letters are not the same. A cover letter identifies an item being sent, the person to whom it is being sent, and the reason for its being sent. A cover letter provides a permanent record of the transmittal for both the writer and the reader.
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."