[otrs] Postmaster Filter changing Ticket State

Hello everybody, I'm currently using 2.3.4 version of OTRS and I have two questions about ticket states. - Is there a way to prevent reopen of a ticket when it has been closed by an agent ? (don't reopen the ticket when user reply Thank you for example). - I am trying to use postmaster filter to assign a particular state to a ticket when user reply "Validation OK" in the body of the mail but it doesn't work. I used : Body => (Validation OK) Assign X-OTRS-State => Closed Thank you Thierry