[otrs] no change state ticket (new open)

Good morning, I have a question, I would change the behavior of OTRS, the following occurs: an agent and attended and confirmed with the client completing a ticket, but after a while the client sends a mail using the last post used by OTRS , which makes the ticket back to the open state and reset the time, could help to avoid this behavior and prevent re-open the ticket. Julio Angulo