Reply Incoming email creates new discussion?

Question

I can create a new topic by email but cannot create a Reply by email for same discussion. Once I get the alerts email from the discussion board.  If reply to the the alert with discussion board email id. It is creating new discussion thread. But I want be reply to same discussion thread that alert came.

1.       If I reply to the approved discussion, It is creating new discussion thread in Discussion board.

2.      2.        If I reply to the pending discussion, I am able to see reply to the thread. i.e. If I reply to same approved alert discussion email, the reply I can  see in newly created discussion that status is pending.

How can I approach this?

---

Jamsbond