I know it's tempting to answer emails because it seems rude or too passive to just ignore them. The truth is that no matter what your response is, to many people ANY response as a sign of interest. So don't even open the messages and delete immediately. You're never obligated to respond to unwanted emails or messages.

Men (and now more women) know this, and while I don't think it's the best way to go about breaking up with someone, it one reason why people some people we've been dating suddenly "disappear" from contact. The truth is that any response, and actually even reading the message, gives the other person a sense of hope.

As females we're socialized to be polite and put other people's feelings before our own, so it's harder for us to just ignore messages and emails. But you have to. One response of "do not message me anymore" sometimes works, but in my experience that can even be taken as encouragement. So after that there should be nothing but radio silence on your part. It may take a while, but if you don't respond (even better to delete the message without reading) eventually they will stop.