Version: (using KDE KDE 3.4.0) I think KMail use the KHTML component to display mails. But I miss a good feature of it. It's auto-scrolling by pressing Shift+Down (one or more time to scroll at different speed, pressing Shift pause the scrolling until next Shift press...). That's interesting when reading long mails.
*** This bug has been marked as a duplicate of 53808 ***