下面的代码可以实现异步发送邮件，等邮件发送出去后会自动调用回调函数，这样在发送邮件时就不会卡住程序不动了

MailMessage m = new MailMessage     ("item@sharejs.com",      "raja@sharejs.com",      "This is the subject for the authorized email.",      "This is the body of the authorized mail!...");      // Send the message using authorization  SmtpClient client = new SmtpClient("smtp.sharejs.com");  client.Credentials = new NetworkCredential("user", "password");  client.EnableSsl = true;      // Add the event handler  client.SendCompleted += new SendCompletedEventHandler(mail_SendCompleted);      // Send the message asynchronously  client.SendAsync(m, null);      // To Cancel the send  //client.SendAsyncCancel();  void mail_SendCompleted(object sender, AsyncCompletedEventArgs e)  {      if (e.Cancelled)          Console.WriteLine("Message cancelled");      else if (e.Error != null)          Console.WriteLine("Error: " + e.Error.ToString());      else          Console.WriteLine("Message sent");  }