c# 邮件发送

        /// <summary>
        /// 邮件发送
        /// </summary>
        /// <param name="subject">邮件标题</param>
        /// <param name="body">邮件内容，html格式</param>
        /// <param name="tomaillist">收件人，支持多人</param>
        /// <returns></returns>
        public async task sendmailasync(string subject, string body, list<string> tomaillist)
        {
            try
            {
              
                smtpclient smtpclient = new smtpclient();
                smtpclient.deliverymethod = smtpdeliverymethod.network;//指定电子邮件发送方式
                smtpclient.host = "smtp.exmail.qq.com";//指定smtp服务器
                smtpclient.credentials = new networkcredential(_username, _pwd);//用户名和密码
                smtpclient.enablessl = true;
                mailaddress fromaddress = new mailaddress(_username);//用户名和密码
                mailmessage mailmessage = new mailmessage();
                mailmessage.from = fromaddress;
                tomaillist.foreach(e =>
                {
                    mailmessage.to.add(e);
                });
                mailmessage.subject = subject;//主题
                mailmessage.body = body;//内容
                mailmessage.bodyencoding = encoding.default;//正文编码
                mailmessage.isbodyhtml = true;//设置为html格式
                mailmessage.priority = mailpriority.normal;//优先级
                await smtpclient.sendmailasync(mailmessage);
            }
            catch (exception ex)
            {
               throw ex;
            }
        }

  public static string addemailbody(string username,string upwd )
        {
            stringbuilder sbbody = new stringbuilder();
            sbbody.append($"<div style=\"text-align:left\">感谢您使用本服务，您的登录账号已经开通：<br/>" );
            sbbody.append($"您可使用账号：{username}，初始密码：{upwd}，登录url：http://***.com<br/>");
            sbbody.append($"用户名、密码均为重要信息，请妥善保管，不得泄露给他人，若出现信息泄露等情况，请及时联系我们。<br/></div>");
            sbbody.append($"<div style=\"text-align:right\">{datetime.now.tostring("yyyy年mm月dd日")}</div>");

            return sbbody.tostring();
        }