Version: 2.0 beta1 (using KDE 4.5.0) OS: Linux The header uses a non-system font size. Changing the font size in the KMail settings doesn't affect this at all. See attached screenshot for details. Compare the font size of the mailheader with the font sizes in the menu etc. Reproducible: Always
You forgot to add screenshot. Regards
Created attachment 50615 [details] Screenshot showing the too large fonts in the mail header. Oups. There it is.
Testing with KDE/4.9 I can not reproduce this. the message header (fancy headers as in your screenshot) uses either the system general font or, if user defined in kmail, the font for the message body