发送电子邮件

public class EmailNotificationService
    {
        /// <summary>

        /// 构造一个邮件通知服务类的实例。

        /// </summary>

        /// <param name="smtpService">SMTP服务器的IP地址</param>

        /// <param name="enableSSL">是否使用SSL连接SMTP服务器器</param>

        /// <param name="port">SMTP服务器端口</param>

        /// <param name="loginName">用于登录SMTP服务器的用户名</param>

        /// <param name="password">登录密码</param>
        private readonly string m_smtpService;
        private readonly string m_loginName;
        private readonly string m_password;
        private readonly bool m_enableSSL;
        private readonly int m_port;
        public EmailNotificationService(string smtpService,bool enableSSL,int port,string loginName,string password)
        {
            this.m_smtpService = smtpService;
            this.m_password = password;
            this.m_loginName = loginName;
            this.m_enableSSL = enableSSL;
            this.m_port = port;
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="sendName"></param>
        /// <param name="address"></param>
        /// <param name="title"></param>
        /// <param name="content"></param>
        public void SendTo(string sendName,string address,string title,string content)
        {
            MailMessage mail = new MailMessage();
            mail.To.Add(address);
            mail.From = new MailAddress(this.m_loginName, sendName, Encoding.UTF8);
            mail.Subject = title;
            mail.Body = content;
            mail.BodyEncoding = Encoding.UTF8;
            mail.IsBodyHtml = false;
            mail.Priority = MailPriority.Normal;

            SmtpClient smtp = new SmtpClient();
            smtp.Credentials = new NetworkCredential(this.m_loginName, this.m_password);
            smtp.Host = this.m_smtpService;
            smtp.EnableSsl = this.m_enableSSL;
            smtp.Port = this.m_port;
            try
            {
                smtp.Send(mail);
            }
            catch (SmtpFailedRecipientsException ex)
            {
                for (int i = 0; i < ex.InnerExceptions.Length; i++)
                {
                    SmtpStatusCode status = ex.InnerExceptions[i].StatusCode;
                    if (status == SmtpStatusCode.MailboxBusy ||
                        status == SmtpStatusCode.MailboxUnavailable)
                    {
                        Console.WriteLine("Delivery failed - retrying in 5 seconds.");
                        System.Threading.Thread.Sleep(5000);
                        smtp.Send(mail);
                    }
                    else
                    {
                        Console.WriteLine("Failed to deliver message to {0}",
                            ex.InnerExceptions[i].FailedRecipient);
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception caught in RetryIfBusy(): {0}",
                        ex.ToString());
            }

        }

public class NotificationHandler
    {
        private static readonly NotificationHandler g_instance = new NotificationHandler();

        public static NotificationHandler Instance
        {
            get
            {
                return g_instance;
            }
        }

        public NotificationHandler()
        {
            this.m_lockObject = new object();
            this.m_mailNotifyInfos = new LinkedList<string>();
            this.m_threadEvent = new ManualResetEvent(false);
            this.m_workThread = new Thread(this.ThreadStart);
            this.m_workThread.Start();

        }

        private readonly LinkedList<string> m_mailNotifyInfos;

        private readonly Thread m_workThread;

        private readonly ManualResetEvent m_threadEvent;

        private readonly Object m_lockObject;

        /// <summary>
        ///
        /// </summary>
        /// <param name="mailNotifyInfo"></param>
        public void AppendNotification(string mailNotifyInfo)
        {
            lock (this.m_lockObject)
            {
                this.m_mailNotifyInfos.AddLast(mailNotifyInfo);
                if (this.m_mailNotifyInfos.Count != 0)
                {
                    this.m_threadEvent.Set();
                }
            }
        }
        /// <summary>
        ///  发送邮件线程的执行方法
        /// </summary>
        public void ThreadStart()
        {
            while(true)
            {
                this.m_threadEvent.WaitOne();
                string mailNotifyInfo = this.m_mailNotifyInfos.First.Value;
                EmailNotificationService mailNotificationService = new EmailNotificationService("smtp.163.com",true,587, "loginName@gmail.com", "loginPassword");
                mailNotificationService.SendTo("稿件中心", "halo_maxs@hotmail.com", "稿件状态变更通知", string.Format("{0}你的稿件{1}状态已变更为{2}", "你的email", "测试邮件发送", "等待发送"));
                lock(this.m_lockObject)
                {
                    this.m_mailNotifyInfos.Remove(mailNotifyInfo);
                    if (this.m_mailNotifyInfos.Count == 0)
                    {
                        this.m_threadEvent.Reset();
                    }
                }
            }
        }

protected void sendButton_Click(object sender, EventArgs e)// 触发事件
        {
            NotificationHandler.Instance.AppendNotification("woowoowow");
        }

老是报错  + InnerException {"由于目标计算机积极拒绝，无法连接。 220.181.12.18:587"} System.Exception {System.Net.Sockets.SocketException}

请问是什么原因 --------------------编程问答-------------------- 由于目标计算机积极拒绝，无法连接
说明220.181.12.18不在线，或者587端口被阻滞了。总之就是客户端访问不到220.181.12.18:587 --------------------编程问答-------------------- 1.看看服务器端监听有没有绑定IP地址
2.看看服务器端是否开了什么防火墙，或客户端有没有开什么防火墙。 --------------------编程问答-------------------- 防火墙我都关了.. 服务器端监听有怎样绑定IP地址

补充：.NET技术 ,  C#