when I was trying to use ExchangeService to get the email from the Inbox, get the error: The request failed. Unable to connect to the remote server

this code can excuted success on my local machine, but got this error when I ran this on the test running client.  below is my code:

            ServicePointManager.ServerCertificateValidationCallback = CertificateValidationCallBack;
            ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
            service.Credentials = new NetworkCredential("testaccount", "passwd", "domain");
            service.AutodiscoverUrl("testaccount@company.com", RedirectionUrlValidationCallback);

            Microsoft.Exchange.WebServices.Data.SearchFilter.SearchFilterCollection sfcol = new SearchFilter.SearchFilterCollection();
            sfcol.Add(new SearchFilter.ContainsSubstring(EmailMessageSchema.Subject, title));
            
            sfcol.Add(new SearchFilter.IsGreaterThanOrEqualTo(MeetingMessageSchema.DateTimeReceived, twoMinutesBeforeNow));
            sfcol.Add(new SearchFilter.IsLessThanOrEqualTo(MeetingMessageSchema.DateTimeSent, now));

            try
            {
                FindItemsResults<Item> findResults = service.FindItems(WellKnownFolderName.Inbox, sfcol, new ItemView(1));

                service.LoadPropertiesForItems(findResults, PropertySet.FirstClassProperties);

                if (findResults.Items != null && findResults.Items.Count > 0)
                {                    
                    emailDetail = new Dictionary<string, string>();
                    emailDetail.Add(EmailTitle, title);
                    emailDetail.Add(EmailBody, findResults.Items.Last().Body.ToString());
                    emailDetail.Add(EmailToList, findResults.Items.Last().DisplayTo);

                }
            }
            catch (Exception ex)
            {
                Logger.Instance.WriteWarning(ex.Message);
                Logger.Instance.WriteWarning("Did not get the email!!!");
            }

            if (EmailDetails == null)
                EmailDetails = new Dictionary<string, Dictionary<string, string>>();
            if(!EmailDetails.ContainsKey(responderid) && emailDetail != null)
                EmailDetails.Add(responderid, emailDetail);

                
        private static bool RedirectionUrlValidationCallback(string redirectionUrl)
        {
            // The default for the validation callback is to reject the URL.
            bool result = false;

            Uri redirectionUri = new Uri(redirectionUrl);

            // Validate the contents of the redirection URL. In this simple validation
            // callback, the redirection URL is considered valid if it is using HTTPS
            // to encrypt the authentication credentials. 
            if (redirectionUri.Scheme == "https")
            {
                result = true;
            }

            return result;
        }



        private static bool CertificateValidationCallBack(object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate,
                                                          System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors sslPolicyErrors)
        {
            // If the certificate is a valid, signed certificate, return true.
            if (sslPolicyErrors == System.Net.Security.SslPolicyErrors.None)
            {
                return true;
            }

            // If there are errors in the certificate chain, look at each error to determine the cause.
            if ((sslPolicyErrors & System.Net.Security.SslPolicyErrors.RemoteCertificateChainErrors) != 0)
            {
                if (chain != null && chain.ChainStatus != null)
                {
                    foreach (System.Security.Cryptography.X509Certificates.X509ChainStatus status in chain.ChainStatus)
                    {
                        if ((certificate.Subject == certificate.Issuer) &&
                           (status.Status == System.Security.Cryptography.X509Certificates.X509ChainStatusFlags.UntrustedRoot))
                        {
                            continue;
                        }
                        else
                        {
                            if (status.Status != System.Security.Cryptography.X509Certificates.X509ChainStatusFlags.NoError)
                            {
                                return false;
                            }
                        }
                    }
                }
                return true;
            }
            else
            {
                return false;
            }
        }

below is the exception:

Exception when trying to execute test : Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. Unable to connect to the remote server ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 10.184.69.27:443
   at System.Net.Sockets.Socket.EndConnect(IAsyncResult asyncResult)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception)
   --- End of inner exception stack trace ---
   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult)
   at Microsoft.Exchange.WebServices.Data.EwsHttpWebRequest.Microsoft.Exchange.WebServices.Data.IEwsHttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult)
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.EmitRequest(IEwsHttpWebRequest request)
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.BuildEwsHttpWebRequest()
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.BuildEwsHttpWebRequest()
   at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest& request)
   at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems[TItem](IEnumerable`1 parentFolderIds, SearchFilter searchFilter, String queryString, ViewBase view, Grouping groupBy, ServiceErrorHandling errorHandlingMode)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems(FolderId parentFolderId, SearchFilter searchFilter, ViewBase view)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.FindItems(WellKnownFolderName parentFolderName, SearchFilter searchFilter, ViewBase view)
   at ........