I discovered a new option in KMail for displaying email headers today. I’m not sure how long it’s been there, but you can now select “Enterprise Headers” for your emails:

KMail with Enterprise Headers
I quite like it, apart from the fact that you can’t have variable-width text in the header and fixed-width text in the body of the email.
3rd March 2010 at 10:08 pm |
How do you make the headers ‘sticky’? Mine keeps reverting to plain.
4th March 2010 at 1:28 am |
I couldn’t tell you, I’m afraid – it just works for me.