SentOnBehalfOfName is tricky. It is usually empty until the item has been sent.
With this code in ThisOutlookSession you should find it blank.
Private Sub Application_ItemSend(ByVal item As Object, Cancel As Boolean)
Dim myRecipient As Recipient
Debug.Print " item.SentOnBehalfOfName - " & item.SentOnBehalfOfName
If item.SentOnBehalfOfName = "someone@somewhere.com" Then
Set myRecipient = item.Recipients.Add("Someone Else")
myRecipient.Type = olCC
item.Recipients.ResolveAll
End If
End Sub
At least one way to get around this:
Sub createSentOnBehalf()
Dim objMsg As mailitem
Set objMsg = Application.CreateItem(olMailItem)
objMsg.SentOnBehalfOfName = "someone@somewhere.com"
objMsg.Display
Set objMsg = Nothing
End Sub
Sub replySentOnBehalf()
Dim objMsg As mailitem
Set objMsg = ActiveInspector.currentItem.reply
objMsg.SentOnBehalfOfName = "someone@somewhere.com"
objMsg.Display
Set objMsg = Nothing
End Sub
Edit: Just realized you could set the cc while creating / replying rather than waiting until ItemSend.
Edit2: Move the cc code from itemsend
Sub createSentOnBehalf()
Dim objMsg As mailitem
Dim myRecipient As Recipient
Set objMsg = Application.CreateItem(olMailItem)
objMsg.SentOnBehalfOfName = "someone@somewhere.com"
Set myRecipient = objMsg.Recipients.Add("Someone Else")
myRecipient.Type = olCC
objMsg.Recipients.ResolveAll
objMsg.Display
Set objMsg = Nothing
End Sub