Version:            (using KDE KDE 3.4.0)
Installed from:    Compiled From Sources

KMail use Up/Down/PageUp/PageDown keys to scroll current message and Left/Right keys to switch choose a message in the list.

After a very long thread on KDE Usability mailing list (in fact, a lot of threads all over the years), a conclusion became obvious.
The actual keybindings in KMail are very good and efficient but, at the same time, distubring at firsts use.

To not remove this advantage of KMail but to increase the usability (read: discoverability) of it there is only one solution: teach the user.

Here is a proposition:

<< Add a small bar between the messages list and the text area.
   This bar will teach and remind to the user what keys to use. >>

Because a picture is always more expressing than a long discourse, that is what the bar should look like:

http://slaout.linux62.org/kde-wishs/kmailSuggestion.png

Mainly:

(Note: the [...] sections are usability reasons why to do so (to keep this report "short").
 To know them, please refer to the "KMail Keyboard Navigation Bar" thread on KDE Usability mailing list.)

- The bar is between the two panes, on by default (even for KMail users for a lot of ages, who could to not know the keys)
- It contains the 4 arrows labeled to inform user how to:
  * Switch messages
  * Scroll current message
- For a better usable interface those buttons:
  * The Up/Down/Left/Right icons SHOULD represent keys for better recognition!
    If there is no such icons, they should be made (we already have the
    "keyboard" or "khotkeys" icon that reepresent a key (at least in Nuvola theme)
    so that's not a big deal).
    [...]
  * Should have a tooltip that say "Use right key to go to previous message"
    for a better learning to the user.
  * Should be pressable as if they were toolbar buttons.
  * If a key is not pressable (Left key if we are on the first message) they
    should be grayed, as in any toolbar.
- The "Navigation Help..." link would popup a "What's This?" like
  popup for more explains.
  [...]
- As shown in the popup, Shift+Left/Right should go to next/prev
  unread message. Because it's a good convenience feature.
  Somewhat better that +/- on notebook computers, where there is no
  numpad, and  +/- as not so obvious if we know Left/Right, using Shift
  is more discoverable in this key.
  But not important: it's a detail. Don't care if it's not implemented.
- Now, what about if a user get confused when pressing Left/Right or
  Up/Down? If he is clever enough he can click the "Navigation Help..."
  link, if he hasn't done it before (because surprised of this link)
- Menus show that "Previous Mail" and "Next Mail" use N and P shortcut keys.
  Those shortcuts should be Left and Right (primary ones to be shown in menus).
  And that would improve the knowledge of the user if he disable the bar.
  For comptability issues, you can make N and P as SECONDARY shortcuts.
  I've done in my KMail that and it's beter!

Here is an example of what should show the "What's This?"-like popup.
It has been modified since the mockup:

| - To browse your message list, use the Leeft and Right arrow keys.
| - Pressing the Shit key when doing so will go to the previous or next unread email.
| - Ctrl+Begin and Ctrl+End allow you to go to the first or last messages in the list.
| - You still can press Up/Down/PageUp/PageDown to scroll the currently displayed message.
| - Press Ctrl+Left or Ctrl+Right to select another folder in the tree.
|   Then, press Ctrl+Space to activate the folder you highlighted.

A thing to correct in KMail: the mail could be activated when doing Ctrl+Begin or Ctrl+End.
Because in the current situation, we must press Right and then Left to select the first/last message we just highlighted.
But this has not been discussed in the kde-usability mailing list.
If there are reasons to not do it...

Now, for the "the bar eats pixels on the screen!" opinion:
[...] Please see mailing list archives if you are interested.