How to retrieve the security descriptor of a message by using the HttpWebRequest class and the HttpWebResponse class in Visual C#

using System;
using System.Net;
using System.IO;   

namespace WebDavNET
{
 /// <summary>
 /// Summary description for Class1.
 /// </summary>
 class Class1
 {
  static void Main(string[] args)
  {
   try 
   {
    // TODO: Replace with the URL of an object on Exchange 2000.
    string sUri = "http://ExchServer/Public/MyFolder/Test.EML";

    System.Uri myUri = new System.Uri(sUri);
    HttpWebRequest HttpWRequest = (HttpWebRequest)WebRequest.Create(myUri);

    string strSDType = "descriptor";
    string sQuery;
    sQuery = "<?xml version='1.0' encoding='utf-8'?>" + 
     "<propfind xmlns=\"DAV:\">" + 
     "<prop xmlns:r=\"http://schemas.microsoft.com/exchange/security/\">" + 
     "<isfolder/>" + 
     "   <r:" + strSDType + "/>" + 
     "</prop>" + 
     "</propfind>";

    // Set credentials.
    // TODO: Replace with appropriate user credentials.
    NetworkCredential myCred = new NetworkCredential(@"DomainName\UserName", "Password");
    CredentialCache myCredentialCache = new CredentialCache();
    myCredentialCache.Add(myUri, "Basic", myCred);
    HttpWRequest.Credentials = myCredentialCache;

    //Uncomment the following statement and comment the previous four statements if you 
    //use Integrated Windows authentication.
    //httpWRequest.Credentials = CredentialCache.DefaultCredentials

    //Note: In Basic type authentication, the user name and password are sent as base64-encoded text and are
    //easily decoded. To help protect the user name and password, we recommend that you
    //use SSL when you use Basic authentication.

    // Set headers.
    HttpWRequest.KeepAlive = false;
    HttpWRequest.Headers.Set("Pragma", "no-cache");
    HttpWRequest.ContentType =  "text/xml";
    HttpWRequest.Headers.Set("Translate", "f");
    HttpWRequest.Headers.Set("Depth", "0");
    HttpWRequest.ContentLength = sQuery.Length;

    //Set the request timeout to five minutes.
    HttpWRequest.Timeout = 300000;
    // set the request method
    HttpWRequest.Method = "PROPFIND";

    // Store the data in a byte array.
    byte[] ByteQuery = System.Text.Encoding.ASCII.GetBytes(sQuery);
    HttpWRequest.ContentLength = ByteQuery.Length;
    Stream QueryStream = HttpWRequest.GetRequestStream();
    // write the data to be posted to the Request Stream
    QueryStream.Write(ByteQuery,0,ByteQuery.Length);
    QueryStream.Close();

    // Send the request and get a response. 
    HttpWebResponse HttpWResponse = (HttpWebResponse)HttpWRequest.GetResponse();
    
    // Get the status code.
    int iStatCode =  (int)HttpWResponse.StatusCode;
    string sStatus = iStatCode.ToString();
    Console.WriteLine("Status Code: {0}", sStatus);
    // Get the request headers
    string sReqHeaders = HttpWRequest.Headers.ToString();
    Console.WriteLine(sReqHeaders);

    // Read the response stream.
    Stream strm = HttpWResponse.GetResponseStream();
    StreamReader sr = new StreamReader(strm);
    string sText = sr.ReadToEnd();
    Console.WriteLine("Response: {0}", sText);

    // Close the stream.
    strm.Close();

    // Clean up.
    myCred = null;
    myCredentialCache = null;
    HttpWRequest = null;
    HttpWResponse = null;
    QueryStream = null;
    strm = null;
    sr = null;
       
   }
   catch (Exception e)
   {
    Console.WriteLine("{0} Exception caught.", e);
   }
  }
 }
}