[otrs] Tickets going to Closed state after emailing customer - after update to 2.3

Hello, I have a problem where we updated from 2.0.4 to 2.3 and now, whenever we send an email to a customer, the ticket is by default put into our "Closed - Successful" state whereas in 2.0.4 an empty email would be default put the ticket in "Client - Pending" state and keep the ticket open. How can we change this behavior? Thank you! Graham