Reference:非同步程序(多執行緒)寄送郵件 (適合大量郵件) @ 就是要紅

Reference:http://www.dotblogs.com.tw/phoenix7765/archive/2008/11/14/5987.aspx

using System;
using System.Net;
using System.Net.Mail;
using System.Text;
using System.Web.UI;

namespace WebApplication
{
public partial class PhoenixMail : BasePage
{
 protected void Page_Load(object sender, EventArgs e)
 {
 }

 protected void btnSend_Click(object sender, ImageClickEventArgs e)
 {
 string[] emaillist = txtTo.Text.Split(','); //將郵件字串分離
 AsyncSendMail delt = new AsyncSendMail(SendMailAsync); //非同步執行
 AsyncCallback acb = new AsyncCallback(SendMailCallBack); //非同步執行
 IAsyncResult isr = delt.BeginInvoke(txtFrom.Text, emaillist, acb, delt); //非同步執行
 ReturnLiteral.Text = "郵件已加入工作排程，完成後會寄送一封通知信給您，謝謝";
 }

 public string SendMailAsync(string From, string[] To) //非同步執行方法主體
 {
 StringBuilder sb = new StringBuilder();
 System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch(); //宣告一個計時器
 sb.AppendFormat("起始時間 - {0} - ", DateTime.Now);
 sb.AppendFormat("總共{0}封郵件", To.Length);

int Success = 0;
int Failure = 0;

SmtpClient emailClient = new SmtpClient("YourMail.com"); //設定SMTP位址
 emailClient.Credentials = new NetworkCredential("YourAccount", "YourPassword"); //設定帳號密碼
 sw.Reset(); //開始計時器
 sw.Start(); //開始計時器
 for (int i = 0; i < To.Length; i++) //一一寄出郵件
 {
 try
 {
 MailMessage message = new MailMessage()
 {
 Body = txtBody.Text,
 BodyEncoding = Encoding.UTF8,
 From = new MailAddress(From),
 IsBodyHtml = true,
 Subject = txtSubject.Text,
 SubjectEncoding = Encoding.UTF8
 };
 message.To.Add(To[i]);
 emailClient.Send(message);
 Success++;
 message.Dispose();
 }
 catch
 {
 sb.AppendFormat("寄送失敗的郵件 - {0}", To[i]);
 Failure++;
 continue;
 }
 }
 sw.Stop(); //計時器停止
 emailClient = null;
 sb.AppendFormat("成功郵件數量：{0}失敗郵件數量：{1}", Success, Failure);
 sb.AppendFormat("結束時間 - {0} - ", DateTime.Now);
 sb.AppendFormat("總共時數 - {0}小時{1}分{2}秒{3}毫秒", sw.Elapsed.Hours, sw.Elapsed.Minutes, sw.Elapsed.Seconds, sw.Elapsed.Milliseconds);
 return sb.ToString(); //回傳訊息
 }
 public delegate string AsyncSendMail(string From, string[] To); //宣告一個非同步委派的方法(與非同步主體簽名碼相同)

    public void SendMailCallBack(IAsyncResult isr)    //非同步回傳訊息的方法
    {
      AsyncSendMail asm = (AsyncSendMail)isr.AsyncState;
      string result = asm.EndInvoke(isr);
      SmtpClient emailClient = new SmtpClient("YourMail.com");
      emailClient.Credentials = new NetworkCredential("YourAccount", "YourPassword");
      MailMessage ResultMail = new MailMessage("YourAccount@YourMail.com", "YourAccount@YourMail.com", "郵件寄送完成通知信", result);
      ResultMail.IsBodyHtml = true;
      emailClient.Send(ResultMail);
      emailClient = null;
      ResultMail.Dispose();
    }
}
}