Reading Pane
Supported on: At least Windows Server 2008 R2 or Windows 7
Registry
HKCU
software\policies\microsoft\office\16.0\outlook\preferences Options
previewmarkmessage boolean previewwaitseconds decimal
- range 1-999 previewdontmarkuntilchange boolean singlekeyreading boolean Description
Checks/Unchecks the option "Mark items as read when viewed in the Reading Pane" in the Reading Pane dialog box.