Open Radar

 
Summary:
The preview pane in Mail can't be closed without a mouse or Trackpad (or Mouse Keys). The closure of the preview pane is important to keyboard users, who can't select messages without highlighting them one after the other and thus marking them read inappropriately.

Steps to Reproduce:
1. Start Mail with the default configuration and add an account.

2. Try navigating the message list from the keyboard without marking mail read. This works with or without VoiceOver commands (which are only effective with VoiceOver on).

3. Or try turning off the preview pane using keyboard commands of any kind.

4. Try using VoiceOver to lower the slider above the message pane.

Expected Results:
A command or preference should be able to close the preview pane. Or, for VoiceOver, lowering the slider should close the pane completely when the slider is dragged beneath 0%.

Actual Results:
With VoiceOver in use, the slider can't be dragged down far enough to close the preview pane. Otherwise, keyboard functionality is missing.

Notes:
Trackpad commander is a very arduous workaround, only applicable if you have a keyboard with a numeric keypad. That workaround makes use of the numpad number 5 and 2 keys held simultaneously when the mouse pointer is routed to the divider. There's no equivalent way to use VoiceOver mouse manipulation commands for that purpose.

This problem has been present since forever, as I recall. The preview pane has always been an imposition, but now that turning it off requires using a classic layout (which I find also provides the best accessibility, being a table view) it's particularly problematic.

AppleVis is tracking this:
http://www.applevis.com/bugs/osx/voiceover-commands-cannot-be-used-close-mails-preview-pane