In the first part, we learned how to configure Active Directory for creating a container in ADSI Edit and to export Service Connection Point (SCP) information from a resource forest to an account forest. In this part, I will discuss how Outlook uses the Autodiscover service to configure user profiles and access mailboxes with other Exchange services such as offline address book (OAB) or (out of office) OOF.

We’ll refer to the same multi-forest environment described in Part 1 of this article series.

Let’s understand step by step how User1’s Outlook configures a mailbox using the Autodiscover service:

  1. User1 logs on to a computer at Green.com and fires Outlook.
  2. Outlook locates the Autodiscover SCP pointer record from the local account forest Active Directory and uses the pointer LDAP URL information to locate the SCP of the resource forest. SCP has information about the Autodiscover URL in the attribute ServiceBindingInformation.
  3. Outlook uses the Autodiscover URL to authenticate and connect to the Autodiscover service of the CAS server.Autodiscover is a virtual directory, which is created in IIS on all of the (Client Access Server) CAS machines in the organization. Below is the reference snapshot.
    Autodiscover folder in IIS
    Autodiscover folder in IIS
  4. Outlook places the XML file request with the Autodiscover service.
  5. The Autodiscover service places the request with the Autodiscover Outlook provider.
  6. The Autodiscover Outlook provider determines where the request is coming from (either internal or external):
    If the connection is coming from the Internet network, the Outlook RPC connection request is placed.
    If the Autodiscover request is coming from an internal client, it returns details such as the user’s display name, internal and external connection settings, location of the user’s mailbox, Outlook Anywhere settings, and the URLs of OOF, OAB, and the Availability service. This information is packed into an XML file and sent back to the Outlook client. Outlook uses this XML file to find all the necessary Internal URLs for making the connection.
  7. Outlook talks to the CAS server at the RPC Endpoint mapper on port 135. The CAS server responds with an appropriate port number of the RPC and Address Book service.
  8. Outlook uses the received port number information and communicates with the RPC and Address book service configured on the CAS server to access the mailbox and address book.
  9. Outlook creates a profile and connects to the other URLs, such as OOF, OAB, and the Availability service from XML file, to access other Exchange server resources.
  10. Once the Outlook profile is created and configured, Outlook tries to contact the Autodiscover service every hour to get the latest XML file. If any URL changes are made at the CAS servers, Autodiscover returns the updated XML file and the same will be updated at the Outlook client.
  11. If user is coming from Internet/external network, Outlook relies on DNS to find the XML file. The XML file location is based on the users email address used in Outlook. Example, if Krishna@green.com is entered as user email address, Outlook will look for the XML file in the below order
    https://green.com/autodiscover/autodiscover.xml
    https://autodiscover.green.com/autodiscover/autodiscover.xml

Outlook automatic configuration from a client at the Green domain using the Autodiscover service

Outlook automatic configuration from a client at the Green domain using the Autodiscover service

Autodiscover test at the Outlook client configured with multiple URLs for multiple services

Autodiscover test at the Outlook client configured with multiple URLs for multiple services

I hope this article helped you understand how Autodiscover works in a multi-forest environment. It’s important to make sure that the necessary trust is configured between the two forests. All Internal URLs on the CAS servers should be configured, and a load balancer should also be configured to allow all the necessary ports with affinity. These settings would help improve not only the performance of Outlook but also the user’s overall experience.

4 Comments
  1. Anonymous 6 years ago

    well done explaining the autodiscover process - precise and to the point. Thanks.

  2. Jason 6 years ago

    well done explaining the autodiscover process - precise and to the point. Thanks.

  3. santosh choudhary 5 years ago

    Good Article and it helped me a lot to understand the autodiscover process-santosh choudhary

  4. Matt 4 years ago

    Great article. It really helped understand the whole autodiscovery process!
    I have an issue myself and not sure if its autodiscover related. I have 2x separate forests exchange 2013 being in Forest A. Users in forest A can configure outlook fine. In Forest B, users can't configure their outlook (linked mailbox). The problem is that outlook auto configuration stucks at searching (step 2 of your screenshot above). Trying the autodiscover URL through the browser works fine and OWA is also ok.
    Any tips?

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