Promt Warning List External Users, on VB Script to checks for external users

[Zvoni]

That was the suggested sollution by westconn1,

Following the full code.
Probably i missed something, could you please update it in case i missed any variable here?

Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
    Dim objMail As Outlook.MailItem
    Dim objRecipients As Outlook.Recipients
    Dim i As Long
    Dim strRecipientAddress As String
    Dim strPrompt As String
 
    If TypeOf Item Is MailItem Then
       Set objMail = Item
       Set objRecipients = objMail.Recipients
 
       For i = 1 To objRecipients.Count     ' no need to step backwards as you are not removing items from the collection
            strRecipientAddress = objRecipients.Item(i).Address
            domain = Mid(strRecipientAddress, InStr(s, "@"))
            
        Select Case domain
            Case "@my1domain.com", "@my2domain.com", "@my3domain.com", "@my4domain.com", "@my5domain.com"
            Case Else:     rejects = rejects & vbNewLine & strRecipientAddress
        End Select
      Next
         
         If rejects <> "" Then
          strPrompt = "This email will be sent outside of the company to:" & vbNewLine & strRecipientAddress & vbNewLine & "Please check recipient address." & vbNewLine & vbNewLine & "Do you still wish to send?"
            If MsgBox(strPrompt, vbYesNo + vbExclamation + vbMsgBoxSetForeground, "Check Address") = vbNo Then
            Cancel = True
         End If
        End If
    End If
End Sub

Your Problem is in Line 14 the InStr(s, "@")
you don't assign a value to "s"
at a guess: that "s" should be strRecipientAddress