.NET发送邮件遇到问题及解决方法

public class EmailHelper
  {
    /// <summary>
    /// 发送邮件
    /// </summary>
    /// <param name="subject">主题</param>
    /// <param name="body">内容</param>
    public static void SendEmail(string subject,string body)
    {
      var mailFrom = ConfigurationManager.AppSettings["mailFrom"];
      var mailTo = ConfigurationManager.AppSettings["mailTo"];
      var mailCC = ConfigurationManager.AppSettings["mailCC"];
      var smtp = ConfigurationManager.AppSettings["smtp"];
      var smtpPort = Convert.ToInt32(ConfigurationManager.AppSettings["smtpPort"]);
      var emailAount = ConfigurationManager.AppSettings["emailAount"];
      var emailPassword = ConfigurationManager.AppSettings["emailPassword"];

  　　　　 //邮件内容信息
      MailMessage mailMessage = new MailMessage
      {
        From = new MailAddress(mailFrom),
        Subject = subject,
        Body = body,
      };
      mailMessage.To.Add(mailTo);
      mailMessage.CC.Add(mailCC);

  　　　　 //邮箱服务器配置
      SmtpClient smtpClient = new SmtpClient(smtp, smtpPort)
      {
        Credentials = new NetworkCredential(emailAount, emailPassword),
        EnableSsl = true,
      };

  　　　　 //发送邮件
      smtpClient.Send(mailMessage);
    }
  } 

 <appSettings>
  <!--发送人、收件人、抄件人-->
  <add key="mailFrom" value="53xxx1314@qq."/>
  <add key="mailTo" value="89xxxx734@qq."/>
  <add key="mailCC" value="89xxx734@qq."/>

  <!--邮箱服务器主机地址和端口号-->
  <add key="smtp" value="smtp.qq."/>
  <add key="smtpPort" value="25"/>

  <!--发送人邮箱账号密码-->
  <add key="emailAount" value="53xxx1314"/>
  <!--此密码非QQ密码，而是邮箱生成的密码-->
  <add key="emailPassword" value="stxxxxxxxxtscbbb"/>
 </appSettings>