The following worked for my ISP. mail.bellsouth.net and 25 are the SMTP server name and outgoing port number respectively. private void btnTestEmail_Click(object sender, EventArgs e) { try { using (MailMessage message = new MailMessage(myEmail, myEmail, "subject1", "body1")) { SmtpClient mailClient = new SmtpClient("mail.bellsouth.net"); mailClient.UseDefaultCredentials = false; CredentialCache myCache = new CredentialCache(); myCache.Add("mail.bellsouth.net", 25, "Basic", new NetworkCredential(myUserName, myPassword)); mailClient.Credentials = myCache; mailClient.Send(message); } } catch (Exception ex) { MessageBox.Show(ex.Message); } } Good Luck.