QQ 发送邮件

public static string UserName = "";
        public static string UserPass = "";

        /// <summary>
        /// 向用户发送邮件
        /// </summary>
        /// <param name="ReceiveUser">接收邮件的用户</param>
        /// <param name="MailTitle">发送标题</param>
        /// <param name="valiCode">发送的验证码</param>
        /// <returns>bool</returns>
        public static bool sendMail(string ReceiveUser, string MailTitle, string valiCode)
        {
            //保存验证码
            var authCode = valiCode;
            UAP.Session.Set("authCode", valiCode);

            MailAddress toMail = new MailAddress(ReceiveUser);
            MailAddress fromMail = new MailAddress(UserName, "51流量神器");
            MailMessage mail = new MailMessage(fromMail, toMail);
            mail.Subject = MailTitle;
            mail.IsBodyHtml = true;
            mail.Body = "【" + MailTitle + "】您好，您的验证码是：" + valiCode + " ."; ;
            SmtpClient client = new SmtpClient();
            client.Host = "smtp.exmail.qq.com";
            client.Port = 587; //25 端口已被阿里云全面封杀
            client.EnableSsl = true;
            client.UseDefaultCredentials = false;
            client.Credentials = new NetworkCredential(UserName, UserPass);
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            try
            {
                client.Send(mail);
                return true;
            }
            catch(Exception ex)
            {
                Extend.WriteTextLog("SendEmail", ex.Message, DateTime.Now, "Email_Error");
                throw;
            }
        }