You may never get an answer from a lawyer on here... Don't have to be a lawyer to know the answer though.
You won't get a DVO because you were never in a relationship.
A protection order is more difficult to get than a DVO .... Sending an occasional friendly email is not going to be enough to get one, & neither it should .... Call the police, tell them what is going on & see what they suggest. I'm guessing something like... have you tried blocking that persons email.