jmtd → log → geek → Mail appeal

This is an appeal for help with a mail problem I have.

I run an SMTP server, and I am currently running a second SMTP server as a honeypot to try sophisticated spam filtering techniques out on before I commit the live one. In order to determine just how effective the filtering techniques are, I want to record which mails arrive, how they're classified by various tests, whether that classification was correct, etc.

Starting with simply recording where the mail goes, I thought, I'll extract the exim-applied id to the message (which looks something like the emphasised section below:

Received: from murphy.debian.org ([146.82.138.6])
    by ice.alcopop.org with esmtp (Exim 3.36 #1 (Debian))
    id 1DWKon-0006B8-00
    for ; Thu, 12 May 2005 22:02:05 +0100

What is the best way to record either these ids, or alternatively another way of identifying each piece of mail, and therefore keeping track of what tests identify what?