Dim myNameSpace As Outlook.NameSpace

Dim myFolder As Outlook.MAPIFolder

Dim c As Variant, arrC As Variant

arrC = Array(olFolderInbox, olFolderOutbox, olFolderJunk)

Set myNameSpace = Application.GetNamespace("MAPI")

For Each c In arrC

    Set myFolder = myNameSpace.GetDefaultFolder(c)

    Call HideFolderPreviewPane(myFolder)

Next c

End Sub

Sub HideFolderPreviewPane(ByRef thisFolder As Outlook.MAPIFolder)

Dim subFolder As Outlook.MAPIFolder

Set Application.ActiveExplorer.CurrentFolder = thisFolder

Do
    i = i + 1

    DoEvents

Loop Until i = 9999 'Delay

Application.ActiveExplorer.ShowPane olPreview, False

If thisFolder.Folders.Count <> 0 Then

    For Each subFolder In thisFolder.Folders

        Call HideFolderPreviewPane(subFolder)

    Next subFolder

End If

End Sub