Change the code to
Public Sub GetAttachmentList(olItem As MailItem)
Dim aAttach As Attachment
Dim Report As String


    If TypeName(olItem) = "MailItem" Then
        For Each aAttach In olItem.Attachments
            Report = Report & GetAttachmentInfo(aAttach)
        Next
        Call CreateReportEmail("Attachment Report", Report)
    End If
End Sub
and run it from a rule that identifies the incoming messages.