I found events that fire when the user receives a message, or hits the send button, but nothing that fire when the user creates a blank, new email.
You should be able to use the NewInspector event. Example:
Public WithEvents myOlInspectors As Outlook.Inspectors
Private Sub Application_Startup()
Initialize_handler
End Sub
Public Sub Initialize_handler()
Set myOlInspectors = Application.Inspectors
End Sub
Private Sub myOlInspectors_NewInspector(ByVal Inspector As Outlook.Inspector)
Dim msg As Outlook.MailItem
If Inspector.CurrentItem.Class = olMail Then
Set msg = Inspector.CurrentItem
If msg.Size = 0 Then
MsgBox "New message"
End If
End If
End Sub