C#异步发送Email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);
        }