How to scan all message in all Outlook folders with VB macro

I have the Outlook VB macro shown below. It works fine for scanning mail in the currently selected folder. How do I modify it to scan for all messages in all folders?

Public Sub scanFolder()
Dim src As Folder
Dim oItem As Object
Dim propertyAccessor As Outlook.propertyAccessor
Set src = Application.ActiveExplorer.CurrentFolder
Dim strHeader As String

For Each oItem In src.Items
    If TypeOf oItem Is Outlook.MailItem And oItem.Categories <> "" Then
'        Debug.Print "Cat: " + oItem.Categories
        Set propertyAccessor = oItem.propertyAccessor
        header = propertyAccessor.GetProperty("http://schemas.microsoft.com/mapi/proptag/0x007D001E")
        Dim headerLines() As String
        headerLines() = Split(header, vbCrLf)

        Dim thisHeader As Variant

        For Each thisHeader In headerLines
            If InStr(thisHeader, "Message-ID:") > 0 Then
               Debug.Print thisHeader + "~" + oItem.Categories
               Exit For
           End If
        Next
    End If
Next
End Sub

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