Version: (using KDE KDE 3.4.0) Installed from: Compiled From Sources You can scroll the message body in the preview pane pagewise by pressing space. However, if you view the message source (accel: v), you cannot move down pagewise by pressing space -- you have to use pgdown instead. Therefore, I propose, for the sake of consistency, and for improved usability, that the message source windows also allows for scrolling with the space bar.
Works for me in KDE 4.3