Autodiscover for exchange returns error 600 unable to retrieve the server name

Hi

I'm trying to do autodiscover the domain. i'm getting 600 as the error code.

How to get the exact exchange url onces POX autheticates. i'm trying to do this from a store app.

i'm using the code

           String EWSURL = null;
String auDisXML = "<Autodiscover xmlns=\"http://schemas.microsoft.com/exchange/autodiscover/outlook/requestschema/2006\"><Request>" +
      "<EMailAddress>" + "ttt@domain.com" + "</EMailAddress>" +
      "<AcceptableResponseSchema>http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a</AcceptableResponseSchema>" +
      "</Request>" +
      "</Autodiscover>";
               NetworkCredential creditinal = new NetworkCredential
            {
                UserName = "XXX"
                Password = "XXXX"
                Domain = "XXX"
            };

System.Net.HttpWebRequest adAutoDiscoRequest = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create("https://autodiscover.domain.com/AutoDiscover/AutoDiscover.xml");
adAutoDiscoRequest.ContentType = "text/xml";
adAutoDiscoRequest.Method = "Post";
adAutoDiscoRequest.Credentials = creditinal;

byte[] bytes = Encoding.UTF8.GetBytes(auDisXML);

Stream rsRequestStream = await adAutoDiscoRequest.GetRequestStreamAsync();
rsRequestStream.Write(bytes, 0, bytes.Length);


WebResponse adResponse = await adAutoDiscoRequest.GetResponseAsync();
Stream rsResponseStream = adResponse.GetResponseStream();
byte[] resp = new byte[adResponse.ContentLength];
await adResponse.GetResponseStream().ReadAsync(resp, 0, (int)adResponse.ContentLength);
string xml = System.Text.Encoding.UTF8.GetString(resp, 0, (int)adResponse.ContentLength);

response

"<?xml version=\"1.0\" encoding=\"utf-8\"?>\r\n<Autodiscover xmlns=\"http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006\">\r\n  <Response>\r\n    <Error Time=\"17:36:08.8597772\" Id=\"4272682333\">\r\n      <ErrorCode>600</ErrorCode>\r\n      <Message>Invalid Request</Message>\r\n      <DebugData />\r\n    </Error>\r\n  </Response>\r\n</Autodiscover>"

Autodiscover Account Settings
XML response:
<?xml version="1.0"?>
<Autodiscover xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">
<Response xmlns="http://schemas.microsoft.com/exchange/autodiscover/mobilesync/responseschema/2006">
<Culture>en:us</Culture>
<User>
<DisplayName>XXXXXXXX</DisplayName>
<EMailAddress>testi@domain.com</EMailAddress>
</User>
<Action>
<Settings>
<Server>
<Type>MobileSync</Type>
<Url>https://mail.xxx.com/Microsoft-Server-ActiveSync</Url>
<Name>https://mail.xxx.com/Microsoft-Server-ActiveSync</Name>
</Server>
</Settings>
</Action>
</Response>
</Autodiscover>

this is the result i got by using https://testconnectivity.microsoft.com

1)I'm getting error code as 600. and why?

2)Is this not possible to get using POX ??

3)How can i get the details like the url name and the account details.