Recently, I accidentally sent an internal email to a client (fortunately, a forgiving one!).
Since then, I’ve decided to look at ways of avoiding this. It turns out, you can do it with a macro.
Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean) Dim recips As Outlook.Recipients Dim recip As Outlook.Recipient Dim pa As Outlook.PropertyAccessor Dim prompt As String Dim strMsg As String Dim Address As String Dim lLen Const PR_SMTP_ADDRESS As String = "http://schemas.microsoft.com/mapi/proptag/0x39FE001E" Set recips = Item.Recipients For Each recip In recips Set pa = recip.PropertyAccessor Address = LCase(pa.GetProperty(PR_SMTP_ADDRESS)) lLen = Len(Address) - InStrRev(Address, "@") Select Case Right(Address, lLen) Case "cdolive.com", "slipstick.com", "outlookmvp.com" Case Else ' remove case else line to be warned when sending to the addresses strMsg = strMsg & " " & Address & vbNewLine End Select Next If strMsg "" Then prompt = "This email will be sent outside of the company to:" & vbNewLine & strMsg & vbNewLine & "Please check recipient address." & vbNewLine & vbNewLine & "Do you still wish to send?" If MsgBox(prompt, vbYesNo + vbExclamation + vbMsgBoxSetForeground, "Check Address") = vbNo Then Cancel = True End If End If End Sub
Simply list your company’s email domains, and the marco will warn you if you send a message outside of those!
They also provide a tutorial video of how to install the macro.