How Autodiscover Service Works In Exchange

What is Autodiscover?

Autodiscover is one of the exchange features which is introduced with Exchange Server 2007. It helps the users to configure their Mailbox automatically.

Server

How does it work?

Now, we will see what is going on behind the scenes of the Autodiscover. During the installation of Exchange Server, each Exchange Server creates its own SCP(Service connection point) which you can see in "Active Directory Sites and Services".

SCP contains the Exchange Server Autodiscover information. It will help outlook clients to locate Autodiscover information to configure user's mailbox profile.

In Exchange IIS, you can see Autodiscover Virtual Directory which is available for the Autodiscover Settings.

In Exchange PowerShell, execute the following command.

Get-Autodiscovervirtualdirectory

When outlook client opens, it will send LDAP request to the Active Directory.

Outlook Client sends LDAP query to Active Directory to look for SCP points.
Active Directory will send the SCP Connection points to the Outlook Client. It will be a normal XML response from AD.
Outlook, then, sorts the connection points received from the previous request and sends HTTPS DNS Request to Autodiscover URL HTTPS://autodiscover.windowstechpro.com/Autodiscover/autodiscover.xml. If it fails, it will send HTTP request to HTTP://autodiscover.windowstechpro.com/Autodiscover/autodiscover.xml. If that also fails, it will send SRV request to Active Directory. If this too fails, Outlook will fail completely and throw an error.
Autodiscover returns with service connection settings to the client which will be an XML file with all the connection settings.
Outlook client will take all these configuration information to contact Exchange Server. Exchange Server will check for the appropriate mailbox information for the configuration information provided by the outlook client.

Now, we will see how it is happening for the outlook which got configured earlier in the article. Fiddler is the great tool to trace HTTP traffic. It helps in troubleshooting or tracing the Autodiscover issues.

Outlook Client sends first LDAP Query to domain. It failed...
It sends Autodiscover request to Active Directory that checks the certificate of Autodiscover.

You can see there is no cookie sent to the browser.

Autodiscover sends the Outlook settings and configuration information to Outlook client.

It contains the authentication information and also, you can see the session cookie passed to the client.

It sends all the EXCH, WEB, and EXPR information to the Outlook client.

Outlook takes the configuration information provided by Autodiscover and contacts the Exchange environment to configure the Mailbox. Also, it downloads the Outlook Offline Address Book (OOB) and EWS settings to post the Outlook profile configuration.

That is it. Today we learned how Autodiscover works. In my upcoming article, we will see the troubleshooting when Autodiscover fails.