Now I got a problem, _guest what_

The Truth is: I want to send the email arrival notification when email arrives
inside. Since the maildrop is the primary delievery agent, I wanna add some
codes at the end of the maildrop to forward part of the message information to a
TCP, UDP whatever ports for other programs use. So the user can get the instant
message arrival notification.

Now the problem is: I really can not locate the right place to add the
codes(getting email information, selecting right place in maildrop or
courierlocal, courierdeliever), please give me some clue on how to do it, OK?

Thank you! and I am looking forward to your response!