Option Explicit
Sub AddCC()
Dim oFolder As Folder
Dim olItem As MailItem
    Set oFolder = Session.GetDefaultFolder(olFolderOutbox)
    For Each olItem In oFolder.Items
        If InStr(1, olItem.To, "someone@somewhere.com", vbTextCompare) > 0 Then
            olItem.CC = "someoneelse@somewhere.com"
            olItem.Send
        End If
    Next olItem
lbl_Exit:
    Set oFolder = Nothing
    Set olItem = Nothing
    Exit Sub
End Sub