MAPI clients wishing to get the correct Autodiscover settings for Exchange 2013 need to get the EXHTTP nodes in the Autodiscover response to configure the client correctly. However, the Plain Old XML (POX) Autodiscover will not return this information if the client is not above a certain version of Outlook. Furthermore, the authentication packages may appear as NTLM or Nego2 instead of Negotiate if the client doesn't claim to be hosted on Windows 7 or greater. This is a known issue in Exchange 2013 and will be fixed in a future version of the product.
[Edit: 10/2/2014]- This has been fixed in Exchange 2013 CU6. You can read about how to use the new header “X-ClientCanHandle” here:
POX Autodiscover request for Exchange
MAPI | CDO client cannot connect to Exchange Server 2013