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."
To save your reader time and to call attention to your strengths as a candidate, state your objective directly at the beginning of the letter. Example: I am seeking a position as a manager in your Data Center. In such a management position, I can use my master’s degree in information systems and my experience as a programmer/analyst to address business challenges in data processing. If you have been referred to a company by one of its employees, a career counselor, a professor, or someone else, mention that before stating your job objective.