When you enable autodiscovery to automatically discover the Microsoft Exchange ActiveSync server in your environment, consider the following guidelines:

• Make sure that Microsoft Exchange Autodiscover is set up correctly. For more information, see the Microsoft documentation for Microsoft Exchange.
• In a Microsoft Exchange environment: Make sure that the autodiscover URL routes to one of the Exchange client access server (CAS) servers. If your environment uses a load balancer, make sure that the Auto Discover URL routes to the load balancer and then route it to your group of CAS servers.
• In a mixed Microsoft Exchange environment (for example, Microsoft Exchange Server 2016 and 2019) environment: Make sure that the autodiscover URL routes to the latest version of the CAS servers (for example, the Microsoft Exchange Server 2019).
• In a cloud-based Microsoft Exchange environment: the autodiscover URLs are typically managed by Microsoft, however if your environment migrated your domain to a cloud-based Microsoft Exchange, make sure that the domain autodiscover URL routes to Microsoft's autodiscover URL (for example, https://autodiscover-s.outlook.com). In the DNS admin portal, make sure a CNAME record is created and that it redirects https://autodiscover.<domain>/autodiscover/autodiscover.xml or https://autodiscover.<domain>/autodiscover/autodiscover.svc to https://autodiscover-s.outlook.com.
• In a cloud-based Microsoft Exchange hybrid environment: mailboxes can exist in both on-premises Microsoft Exchange and cloud-based Microsoft Exchange. Make sure that the autodiscover URL routes to the on-premises Microsoft Exchange Server.