Send mail from gmail C# Asp.Net

  MailMessage mail = new MailMessage();
       mail.To.Add(txtUM.Text);
       mail.From = new MailAddress("pavan.it30@gmail.com");
       mail.Subject = "Welcome To NL SOFTTECH SERVICES!!";
       string Body = "User ID :"+txtUI.Text+" Password :"+txtPass.Text;
      mail.Body = Body;
      mail.IsBodyHtml = true;

      //mail.Attachments.Add(
          SmtpClient smtp = new SmtpClient();
     smtp.Host = ConfigurationManager.AppSettings["SMTP"];
       smtp.Credentials = new System.Net.NetworkCredential(ConfigurationManager.AppSettings["FROMEMAIL"], ConfigurationManager.AppSettings["FROMPWD"]);
      smtp.EnableSsl = true;  
     smtp.Send(mail);
     Label1.Text = "Mail Sent Successfully";


and add this tag in web.config


<appSettings>
    <!--<add key="SMTP" value="smtp.gmail.com"/>
    <add key="FROMEMAIL" value="pavan.it30@gmail.com"/>
    <add key="FROMPWD" value=""/>-->
  </appSettings>