[otrs] interaction using email only

Somebody can help me ? How to set Interaction between agent and customer base on email ? It run when i'm using version 1.3, that only need an email to update the ticket. So, customer open new ticket using an email, the ticket send to all agent in queue group, and agent only need to reply that email, and the ticket is updated. With this condition, I can put a filter that can read special tag from 'subject' to make an action like 'Close Ticket'. But now only notification is send by system, but not the ticket itself. I'm using otrs 2.2.6 Anyone know how to make it working again ? M. Prasodjo