Sub PreviousSheet()
    On Error Resume Next
    ActiveSheet.Previous.Select
End Sub

Sub NextSheet()
    On Error Resume Next
    ActiveSheet.Next.Select
End Sub

Sub test()

    Dim olApp As Outlook.Application
    Set olApp = GetOutlookApp()

    'I think this is how to loop through the open items?
    For i = olApp.Inspectors.Count To 1 Step -1
        Set olItem = olApp.Inspectors.Item(i).CurrentItem
        olItem.Select 'How do I set focus?
    Next i

End Sub

Function GetOutlookApp() As Outlook.Application
     ' returns reference to native Application object
    Set GetOutlookApp = Outlook.Application
End Function

Sub GetPreviousOpenItem()

    Set MainWindow = Application.ActiveExplorer

    Dim olApp As Outlook.Application
    Set olApp = GetOutlookApp()

    If olApp.ActiveInspector Is Nothing Then
        Exit Sub
    End If

    ActiveInspectorIndex = GetIndexOfActiveInspector(olApp, olApp.ActiveInspector)

    If ActiveInspectorIndex - 1 > 0 Then
        Dim PreviousInspector As Inspector
        Set PreviousInspector = olApp.Inspectors(ActiveInspectorIndex - 1)
        olApp.Inspectors(ActiveInspectorIndex - 1).Display
    Else
        olApp.Inspectors(olApp.Inspectors.Count).Display
    End If

    MainWindow.Activate

End Sub

Sub GetNextOpenItem()

    Set MainWindow = Application.ActiveExplorer

    Dim olApp As Outlook.Application
    Set olApp = GetOutlookApp()

    If olApp.ActiveInspector Is Nothing Then
        Exit Sub
    End If

    ActiveInspectorIndex = GetIndexOfActiveInspector(olApp, olApp.ActiveInspector)

    If ActiveInspectorIndex + 1 <= olApp.Inspectors.Count Then
        Dim NextInspector As Inspector
        Set NextInspector = olApp.Inspectors(ActiveInspectorIndex + 1)
        NextInspector.Display
    Else
        olApp.Inspectors(1).Display
    End If

    MainWindow.Activate

End Sub

Function GetIndexOfActiveInspector(olApp, CurrentItem) As Integer

    CurrentItem = olApp.ActiveInspector

    For i = 1 To olApp.Inspectors.Count

        Dim Inspector
        Set Inspector = olApp.Inspectors.Item(i)
        Set olItem = Inspector.CurrentItem

        If olItem Is CurrentItem Then
            GetIndexOfActiveInspector = i
            Exit Function
        End If

    Next i

    MainWindow.Activate

End Function
Function GetOutlookApp() As Outlook.Application
     ' returns reference to native Application object
    Set GetOutlookApp = Outlook.Application
End Function