Adding Email Replies to Tickets

I am not the primary administrator/moderator of my company’s RT system, so I do not have a large base of knowledge from which to feed, but I cannot seem to find an answer to the following question:

When a user replies to our follow-up on a ticket, how can that reply (as long as it still contains the ticket information in the subject, obviously) automatically be added to the existing ticket? As of now, all ticket replies are simply marked as read by RT, and ignored, and we have to pool our entire inbox regularly for replies to our follow ups for all tickets. This does not allow for efficient tracking, yet I can not seem to find a very good answer anywhere. Perhaps I am not searching with the right terms.

Could someone please shed some light on this subject for me, as I would love to assist in streamlining this process as much as possible.

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