private void SendMail()
  {

    //Create message object and populate with the data from form
    System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage();
    message.From = new System.Net.Mail.MailAddress(txtFrom.Text.Trim());
    message.To.Add(txtTo.Text.Trim());
    message.Subject = txtSubject.Text.Trim();
    message.Body = txtBody.Text.Trim();

    //Setup SmtpClient to send email. Uses web.config settings.
    System.Net.Mail.SmtpClient smtpClient = new System.Net.Mail.SmtpClient();

    //Error handling for sending message
    try
    {
      smtpClient.Send(message);
      //Exception contains information on each failed receipient
    }
    catch (System.Net.Mail.SmtpFailedRecipientsException recExc)
    {
      for (int recipient = 0; recipient < recExc.InnerExceptions.Length - 1; recipient++)
      {
        System.Net.Mail.SmtpStatusCode statusCode;
       
        statusCode = recExc.InnerExceptions[recipient].StatusCode;

        if ((statusCode == System.Net.Mail.SmtpStatusCode.MailboxBusy) || (statusCode == System.Net.Mail.SmtpStatusCode.MailboxUnavailable))
        {
          
          System.Threading.Thread.Sleep(5000);
          smtpClient.Send(message);
        }
        else
        {
            ErrorLabel.Text = recExc.Message;

          
        }

      }
    }
    //General SMTP execptions
    catch (System.Net.Mail.SmtpException smtpExc)
    {
      
        ErrorLabel.Text = smtpExc.StatusCode.ToString();
    }
    catch (Exception ex)
    {
      //Log error to event log.
    }
  }

< system.net>
		< mailSettings >
			< smtp >
				< network host="YOUR HOST INFO HERE"/ >
			< /smtp >
		< /mailSettings >
< /system.net >