异步发送电子邮件代码

/// <summary>          /// 异步发送电子邮件          /// </summary>          /// <param name="fromEmail">发送方电子邮件</param>          /// <param name="fromPwd">发送方电子邮件密码</param>          /// <param name="toEmail">接收方电子邮件</param>          /// <param name="subject">邮件标题</param>          /// <param name="body">邮件内空</param>          /// <param name="emailType">邮件类型</param> smtp.163.com.cn; smtp.qq.com.cn; smtp.126.com.cn;  smtp.sina.com.cn          private void SendEmailAsync(string fromEmail, string fromPwd, string toEmail, string subject, string body, string emailType)          {              MailAddress addrFrom = new MailAddress(fromEmail, fromEmail);              MailAddress addrTo = new MailAddress(toEmail, toEmail);              MailMessage mm = new MailMessage(addrFrom, addrTo);              mm.BodyEncoding = Encoding.UTF8;              mm.IsBodyHtml = true;              mm.Subject = subject;              mm.Body = body;                 if (!string.IsNullOrEmpty(attFile))              {                  Attachment att = new Attachment(attFile, MediaTypeNames.Application.Octet);                  ContentDisposition cd = att.ContentDisposition;                  cd.CreationDate = File.GetCreationTime(attFile);                  cd.ModificationDate = File.GetLastWriteTime(attFile);                  cd.ReadDate = File.GetLastAccessTime(attFile);                  mm.Attachments.Add(att);//添加附件              }                 NetworkCredential nc = new NetworkCredential(fromEmail, fromPwd);              SmtpClient smtp = new SmtpClient(emailType);              smtp.UseDefaultCredentials = false;              smtp.Credentials = nc;              smtp.EnableSsl = false;              smtp.DeliveryMethod = SmtpDeliveryMethod.Network;              smtp.SendCompleted+=new SendCompletedEventHandler(smtp_SendCompleted);              smtp.SendAsync(mm, "OK");          }             void smtp_SendCompleted(object sender, AsyncCompletedEventArgs e)          {              if (e.UserState.ToString() == "OK")                  MessageBox.Show("发送成功!", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);          }