Sometimes a person's gender is unclear from a name _ names like "Corey" or "Blake," are both common women's and men's names. If that is the case, do some investigating to determine gender from searching on LinkedIn or a company website. But if it remains ambiguous, simply write out the person's full name, dropping the title. For example, "Dear Corey Meyer."
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.