EWS Autodiscover Process in Hybrid with "internal" Exchange Servers

The behavior you are seeing is expected in a hybrid Exchange configuration. Autodiscover does not return the hybrid server URL when the mailbox is located on-premises. Instead, Autodiscover always routes the request to the server that hosts the mailbox, which is why the response includes the internal EWS URL.

The Hybrid server doesn’t act as a proxy that rewrites or replaces Autodiscover responses. It simply redirects the request to the mailbox server, and the mailbox server publishes only its internal URLs because it was never configured with external EWS endpoints.

This explains why the connectivity analyzer and Teams integration try to resolve mail.contoso.internal. Clients outside the internal network cannot use this endpoint, so the connection fails.

To resolve the issue, the internal Exchange servers must have valid external EWS URLs defined in their virtual directory configuration, even if they are intended to serve internal users only. In a hybrid environment, workloads such as Teams rely on externally reachable EWS endpoints to open shared calendars or free/busy.

If the internal servers cannot be modified to publish an external FQDN, the hybrid coexistence will continue to fail for cross-premises scenarios because Autodiscover will always return the mailbox server details, not the hybrid server’s external URL.