测试服务器SMTP是否可用

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace SeverEmailTest
{
    public partial class Main_Frm : Form
    {
        System.Net.Mail.MailMessage TheMail;

        public Main_Frm()
        {
            InitializeComponent();
        }

        private void bt_Send_Click(object sender, EventArgs e)
        {
            TheMail = new System.Net.Mail.MailMessage();
            TheMail.From = new System.Net.Mail.MailAddress("Jack@XXXX.com", "Jack China");

            string[] _addresses = txt_AddressTo.Text.Split(';');

            foreach (string _item in _addresses)
            {
                if (string.IsNullOrEmpty(_item) == false)
                {

                    if (isEmailAddress(_item) == false)
                    {

                        MessageBox.Show( "the email address : " + _item + " is invalid");
                        return;
                    }
                    TheMail.To.Add(_item);
                }
            }
            if (TheMail.To.Count == 0)
            {
                TheMail.To.Add("jacks@XXXX.com");
            }
            string SMTPServer = this.txt_SMTP.Text.Trim();
            if (string.IsNullOrEmpty(SMTPServer))
            {
                SMTPServer = "LocalHost";
            }

            TheMail.Subject = string.Format("This is a test email from {0},the smptp {1} is ok", Environment.MachineName, SMTPServer);
            TheMail.Body = txt_Content.Text ;

            TheMail.IsBodyHtml = false;
            TheMail.BodyEncoding = Encoding.UTF8;
            TheMail.Priority = System.Net.Mail.MailPriority.Normal;

            string _result = "";

            try
            {
                System.Net.Mail.SmtpClient smtpClient = new System.Net.Mail.SmtpClient();
                if (SMTPServer != "")
                {
                    smtpClient.Host = SMTPServer;
                }

                string smtpUserName = System.Configuration.ConfigurationManager.AppSettings["SmtpUserName"];
                string SmtpPassword = System.Configuration.ConfigurationManager.AppSettings["SmtpPassword"];

                if (string.IsNullOrEmpty(smtpUserName) == false && string.IsNullOrEmpty(SmtpPassword) == false)
                {
                    smtpClient.Credentials = new System.Net.NetworkCredential(smtpUserName, SmtpPassword);
                }
                smtpClient.Send(TheMail);
                _result = "Successfully";
            }
            catch (Exception ex)
            {

                _result = ex.Message + "--" + ex.InnerException + "--" + ex.StackTrace;
            }
            MessageBox.Show(_result);
          

        }

        public  bool isEmailAddress(string address)
        {
            //string expr = @"^[a-z0-9A-Z_\-\.]+[@]{1}[a-z0-9A-Z_\-\.]+[\.]{1}[a-z0-9A-Z_\-\.]+$";
            string expr = @"((^[a-zA-Z0-9]+[a-z0-9A-Z_\-\.]*[a-z0-9A-Z_\-]+)|(^[a-zA-Z0-9]+))[@]{1}[a-zA-Z0-9]+[a-z0-9A-Z_\-\.]*[\.]{1}[a-z0-9A-Z_\-\.]*[a-zA-Z0-9]+$";
            System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex(expr);

            bool eval = reg.IsMatch(address);
            if (eval)
            {
                expr = @"\.{2,}";
                reg = new System.Text.RegularExpressions.Regex(expr);
                eval = !reg.IsMatch(address);
            }
            return eval;
        }

        private void bt_Cancel_Click(object sender, EventArgs e)
        {
            System.Environment.Exit(0);
        }
    }
}