If the master degree<span> is the </span>person's<span> job, like a </span>master's degree<span> of science, then use the full post-nominal for that </span>degree<span>, such as “John Doe, M.S.” Write “Dear” on the first page of the letter, followed by the </span>person's<span> title and the </span>person's<span> last name.</span>
It Depends if the person that you are in a relationship is ok with it