使用mailhelper.cs时出现电子邮件问题

我有一个web应用程序,我将它设置为使用mailhelper.cs和web.config设置,通过gmail帐户自动发送电子邮件。我的应用程序已经运行了10天,现在它给了我发送电子邮件的错误和停止。我处理这个错误,它是“发送邮件失败”。内部异常是“试图对无法访问的主机执行套接字操作216.239.59.109:587”,下面是代码:

<mailSettings>
  <smtp from="myemail@gmail.com">
    <network host="smtp.gmail.com"
             port="587"
             userName="myemail@gmail.com"
             password="mypass"/>
  </smtp>
</mailSettings>

using System.Net.Mail;

public class MailHelper
{
   /// <summary>
   /// Sends an mail message
   /// </summary>
   /// <param name="from">Sender address</param>
   /// <param name="to">Recepient address</param>
   /// <param name="bcc">Bcc recepient</param>
   /// <param name="cc">Cc recepient</param>
   /// <param name="subject">Subject of mail message</param>
   /// <param name="body">Body of mail message</param>
   public static void SendMailMessage(string from, string to, string bcc, string cc, string subject, string body)
   {
      // Instantiate a new instance of MailMessage
      MailMessage mMailMessage = new MailMessage();

      // Set the sender address of the mail message
      mMailMessage.From = new MailAddress(from);
      // Set the recepient address of the mail message
      mMailMessage.To.Add(new MailAddress(to)); 
      // Check if the bcc value is null or an empty string
      if ((bcc != null) && (bcc != string.Empty))
      {
         // Set the Bcc address of the mail message
         mMailMessage.Bcc.Add(new MailAddress(bcc));
      }

      // Check if the cc value is null or an empty value
      if ((cc != null) && (cc != string.Empty))
      {
         // Set the CC address of the mail message
         mMailMessage.CC.Add(new MailAddress(cc));
      }       // Set the subject of the mail message
      mMailMessage.Subject = subject;
      // Set the body of the mail message
      mMailMessage.Body = body; 
      // Set the format of the mail message body as HTML
      mMailMessage.IsBodyHtml = true;
      // Set the priority of the mail message to normal
      mMailMessage.Priority = MailPriority.Normal;

      // Instantiate a new instance of SmtpClient
            SmtpClient mSmtpClient = new SmtpClient();
            mSmtpClient.Host = "smtp.gmail.com";
            mSmtpClient.Port = 587;
            mSmtpClient.EnableSsl = true;

      // Send the mail message
      mSmtpClient.Send(mMailMessage);
   }
}