Exchange Server 2007 external autodiscover not working

Question

Dears
I need help to resolve my autodiscover issue externally. Internally everything works fine like auto discover, free-busy, out of office etc.
Our Exchange is 2007 CCR clustered with one CAS and HUB server (both in one) and 2 mailbox servers (active & passive) with a mail gateway appliance instead of Edge Server.
Externally nothing of the above are working but Outlook Anywhere is working and more number of uses are working without any issue. For all these users who connected with Outlook-Anywhere they cannot see free-busy, out of office etc.
Please let me know how I can check the settings for internal and external settings and what all details need to be provided for external autodiscover through cmdlet or GUI. 

Answer 1

I am getting a XML file when accessing above link from external source.
The beginning is as detailed below 
  <?xml
version="1.0" encoding="utf-8" ?>
- <wsdl:definitions
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:s="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
- <wsdl:types>
- <xs:schema
xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:import
namespace="http://schemas.microsoft.com/exchange/services/2006/messages" schemaLocation="messages.xsd"
/>
  </xs:schema>
  </wsdl:types>
- <wsdl:message
name="ConvertIdSoapIn">
  <wsdl:part
name="request"
element="tns:ConvertId" />
  <wsdl:part
name="RequestVersion"
element="t:RequestServerVersion" />
  </wsdl:message>
- <wsdl:message
name="ConvertIdSoapOut">
  <wsdl:part
name="ConvertIdResult"
element="tns:ConvertIdResponse" />
  <wsdl:part
name="ServerVersion"
element="t:ServerVersionInfo" />
  </wsdl:message>
- <wsdl:message
name="GetFolderSoapIn">
  <wsdl:part
name="request"
element="tns:GetFolder" />
  <wsdl:part
name="Impersonation"
element="t:ExchangeImpersonation" />
  <wsdl:part
name="S2SAuth"
element="t:SerializedSecurityContext" />
  <wsdl:part
name="MailboxCulture"
element="t:MailboxCulture" />
  <wsdl:part
name="RequestVersion"
element="t:RequestServerVersion" />
  </wsdl:message>
- <wsdl:message
name="GetFolderSoapOut">
  <wsdl:part
name="GetFolderResult"
element="tns:GetFolderResponse" />
  <wsdl:part
name="ServerVersion"
element="t:ServerVersionInfo" />
  </wsdl:message>