SCP lookup – SCP = Service Connection Point. SCP  is an Active Directory object that provides connection points for various apps. Outlook will try to find an "internal domain" server (Windows Server on local network; a.k.a. "on-premise" Windows Server (which may or may not be running Exchange) to get Autodiscover information from Active Directory. It tries an LDAP query to Active Directory Domain Services (AD DS) to retrieve Autodiscover SCP objects. If that fails, Outlook begins it’s “non-domain” connected logic and will go then in order down this list. If it succeeds because Outlook is on an "internal domain" server, it could set up the user's Outlook with whatever it finds.

    HTTPS root domain query – Outlook, if not "domain joined" (remember that "internal domain" server?), uses the RIGHT HAND SIDE (after the @) of the users SMTP address to do this query.

    HTTPS Autodiscover domain query – If the above search yields no response, the next URL Outlook will try is: https://autodiscover.rackspace.com/autodiscover/autodiscover.xml

     HTTP redirect method - external lookup for: 1) https://domain.tld/autodiscover.autodiscover.xml 2) https://autodiscover.domain.tld/autodiscover.autodiscover.xml

    SRV record query - external lookup for: _autodiscover._tcp.domain.tld

    Local XML file (You can create a local XML file for Outlook clients.  It will force Outlook to use whatever is in the XML file for autodiscover settings.)

    Cached URL in the Outlook profile (new for Outlook 2010 version 14.0.7140.5001 and all later versions)