ServiceDesk email responses

Is there a way to stop a user from replying to a closed incident, and give them a message the incident has already been closed? We close tickets after we can't contact them for 3 days in a row, and sometimes they will reply a month later. We would rather have a reponse telling them to enter a new ticket. If not, is there a way to differentiate between an email response to say if the ticket is open or closed? Meaning when the email alert comes into the mailbox saying the incident # has received an email response, can it tell us which tickets are closed?

Thanks,

Steven