How Autodiscover works in Exchange Online, Exchange On-Premise and Hybrid Exchange – Part 2

December 24th, 2018 | Posted by admin in Exchange

On the last part, we saw how the auto discover works for internal and external clients. In this post we will see how the Autodiscover working on Exchange Online.

How Autodiscover works in Exchange Online?

If a company has their messaging infrastructure in Office 365 alone without any On-Premise infrastructure, this is how the Autodiscover works for Exchange Online Mailbox

  1. When user enters the credential, it will perform a SCP query and it will fail
  2. DNS lookup will happen to find the Autodiscover service for the FQDN autodiscover.domainname.com
  3. Once it finds the Autodiscover record, there will be CNAME record created for Autodiscover pointed to Autodiscover.outlook.com. Here it is pointed to connect Exchange Online to get the Autodiscover information
  4. Outlook will connect autodisover.outlook.com (Exchange Online) and the credential will be validated.
  5. Autodiscover xml file will be returned to outlook client with the server name to connect as outlook.office365.com

Below test connection result show the details on how it worked. For testing, I have directly entered the domainname.onmicrosoft.com email address, so the SCP query is not available on the below result.

Explanation:

Lot of tools are available to see the behaviour of Autodiscover like Outlook Test E-mail AutoConfiguration, Exchange Remote Connectivity Analyser, Fiddler and outlook advanced logging etc. Here we will use the Outlook Test E-mail AutoConfiguration option to explain the Autodiscover Process.

All the requests to Office 365 are considered as external network request and it behaves the same way as explained in the previous article.

  1. Second portion of the email address is considered as a the fqdn and it try to connect to that Url and it failed

  1. Outlook uses the predefined URL as mention below to connect and it failed again

  1. Searching for any local record for domain name and it failed

  1. Redirection method (HTTP instead of HTTPS to predefined URL) followed and it got response to go to https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml. It will prompt to enter the credential for validation at this point

  1. Got response for https & http of https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml and for xml will retrieved from Exchange Online and outlook configures the profiles

This is how you need to split the log to see how the Autodiscover working on your environment.

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