Tracking numbers

Giganews Newsgroups
Subject: Tracking numbers
Posted by:  slappyhack (slappyha…
Date: Wed, 26 Apr 2006

I need to track emails with a unique tracking number from which I have the tracking number engine running.  I am currently storing this number in the subject of the message and parsing the subject to for the number to add the email to the correct thread.  The problem with this as you probably have already guessed is the subject can be changed by anyone repling to the mesage thus breaking the thread.

So the question I pose is: Is there a place I can add a piece of metadata (my tracking number) that I can parse with logic but not alter with fat fingers?  I do not want to add it to the body of the email but if I have to then I have to.