Mail body munging: state of the art?

[Andy Armstrong]

I'm playing with an idea that I've been mulling over for a while. I  
suppose you could call it a kind of CRM. The idea is that I have a  
mail filter running on my server that can annotate incoming mail in a  
number of ways - the thing I'm playing with for the proof of concept  
is to look the From: address up with the Flickr API and then, if the  
sender has a Flickr account include a link to it at the foot of the  
email. In general I want to use it to attach arbitrary factoids about  
the sender to my incoming mail.

I want to be able to add annotations in a way that works reliably  
regardless of the format of the mail - if it's a multipart mail with  
HTML and plain text versions I'd like to add the annotation to both  
versions for example.

What should I be using? What's the state of the art for parsing /  
modifying / recreating mail?

-- 
Andy Armstrong, hexten.net