That's the reason I don't answer every e-mail I receive as feedback to my stories. I answer every serious question though. I even answered some from anonymous senders before I realized my mistake.
Don't believe I wouldn't appreciate the mails I didn't answer, especially if they were kind or downright flattering. I'm addicted to them and already miss the response from some of my favorite readers.
The feedback I get is my main motivation to continue with the story. I hope you notice the subtle threat (No feedback - no motivation - no story!)