Option Explicit

' The WithEvents keyword specifies that the variable is an object variable
' used to respond to events triggered by an ActiveX object.
Public WithEvents olInboxItems As Outlook.Items

Public Sub Application_Startup()

    On Error Resume Next    ' Deal with errors

    ' Set the object variable to the object whose event you want to handle.
    Set olInboxItems = Outlook.Session.GetDefaultFolder(olFolderInbox).Items

End Sub

Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)

    On Error Resume Next    ' Deal with errors

    Item.Categories = ""    ' Assign Categories property of the object.

End Sub

Private Sub olInboxItems_ItemAdd(ByVal Item As Object)

    On Error Resume Next    ' Deal with errors

    If Item.Class = olMail Then ' Check to make POSITIVE this is email
        Item.Categories = ""    ' Assign Categories property of the object.
        Item.Save   ' Save the object.
    End If

End Sub