Exchange 2013 Autodiscover Service – How it Works?

About Exchange Auto-discovery Service

Working of Auto-discovery Service

Auto-discover service was introduced in Exchange 2007, which provides remote access to Exchange server’s clients using Outlook from anywhere. Exchange Administrators can now configure Outlook usage anywhere with clients using Windows mobile OWA, Outlook 2007, Outlook 2010 or Outlook 2013.This feature automatically configures your user profiles with the server and allows access to features such as offline address book or unified messaging system.

Whenever we install Client Access Server role on Exchange 2010/13 machine, Auto discovery virtual directory is created automatically under Internet Information Service (IIS).

Auto discovery service gets executed in the following conditions:

->Creation of a new Outlook profile or updating them.

->Changes in the network of the messaging environment will trigger auto discovery to make user profile availability.

->Wherever Client Access server role is installed a new SCP (Service Connection point) object is created to locate the Autodiscover Service.

Auto Discovery Service

Service Connection Point(SCP) object contains the following things:

Service binding information:

It has the complete information about Fully Qualified Domain Name (FQDN) of the Client Access Server.

Keywords attribute: 

It specifies the sites to which SCP record is connected.

How does an Outlook client connect to Autodiscover service?

  1. Outlook sends a directory access protocol query to locate SCP objects using NULL value as the hostname. Whenever domain a name is not specified then the operation searches for the global catalog server in the domain on the basis of the membership of the machine initializing the operation.

 2.  Outlook fetches the information and lists the results on the basis of the keyword attribute of the SCP record. Two types of lists are generated: in-site list and off site list. The in-site list contains AutodiscoverSiteScope information present in the SCP records. It is a parameter set by the Client Access Server; the parameter depicts authorities   under Autodiscovery service. This service then matches the information in SCP records for in-site list; if there are no on-site lists then, an off-site list is generated.

 3. Outlook tries to establish a connection to the Autodiscover URL from the in-site lists and then off site list.

    If these fail then it reverts back to default mechanism of contacting predefined URLs using DNS 

  On failure of the above process Outlook uses HTTP redirect methods and then use the SRV record lookup method.

 4. The next step involves Autodiscovery service to obtain the connection settings and URLs for the configured Exchange Services.

5. All the connection settings and URLs export to an XML file, which is then returned as an HTTP response from Autodiscovery service.

6.Outlook manages the settings and then connects to our Exchange messaging environment.

If Outlook is initiated on a machine that is not domain connected then Outlook first tries to locate Autodiscover service .It looks up for Service Connection Point in the Active Directory. Because the client machine is not domain connected, the active directory remains unavailable. It then tries to locate Autodiscover service by DNS lookup using two predefined URLs: