Additional OWA sites redirects to OWA (default web site) - Exchange2016

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Hi @Евгений Котляревский

Please note that we're not Microsoft support, this is a user-to-user support forum. Moderators here don’t have backend access to Microsoft systems, so we can only provide technical guidance based on the public resources.

Based on the behavior you described, this appears to be expected Exchange 2016 behavior rather than a misconfiguration of the additional OWA virtual directories.

The key difference in your environment is that Ex1 and Ex2 host the active mailbox database copies, while Ex3 and Ex4 only host passive copies.

When a user initially connects to Ex1 or Ex2, Exchange can service the OWA session locally, so the user remains on the namespace they originally used (https://mail.compB.com/owa).

However, when a user connects to Ex3 or Ex4, Exchange detects that the mailbox database is active on another server and proxies or redirects the session to the server hosting the active copy. During this process, Exchange generates the destination URL based on the target server’s OWA configuration, which explains why users are redirected to the default namespace (https://mail.compA.com/owa).

Depending on the scenario, Exchange may either proxy the request transparently or issue an HTTP 302 redirect. If you capture a browser/Fiddler trace and see a 302 response with a Location header pointing to https://mail.compA.com/owa, that confirms Exchange is selecting that namespace during routing.

The RedirectToOptimalOWAServer setting is often assumed to control all OWA redirection behavior, but it does not override Exchange’s core client access routing logic. As a result, disabling that setting does not prevent the namespace change in this scenario.

The fact that the issue only occurs when users initially connect to Ex3 or Ex4 is a strong indication that the behavior is related to Exchange routing the session toward the active mailbox server rather than a problem with the additional OWA virtual directory itself.

Before making architectural changes, capturing a trace as mentioned above can help confirm whether Exchange is issuing a redirect versus a proxy response.

From a design perspective, this behavior aligns with how Exchange 2016 client access services are implemented. Microsoft guidance emphasizes simplifying namespace design and reducing the number of namespaces in modern Exchange deployments. The Exchange Preferred Architecture further recommends standardized designs and notes that while other configurations may technically work, they are not the recommended practice.

In practice, Exchange 2016 is designed around a simplified namespace model (typically a single namespace such as mail.contoso.com). While multiple namespaces are technically possible, maintaining separate OWA namespaces across mailbox routing scenarios is not part of the recommended architecture and can lead to behavior like the redirection you are observing.

References:

• Client Access services | Microsoft Learn
• Exchange Server preferred architecture | Microsoft Learn

So, the most reliable approaches are typically:

• Use a single OWA/ECP namespace across all Exchange servers, or
• Implement any namespace separation at the load balancer layer rather than relying on multiple OWA virtual directories.

Based on your description, there is no indication that your additional OWA virtual directories are misconfigured. The behavior you are seeing is consistent with Exchange 2016 routing logic when the initial connection is made to a server that does not host the active mailbox database copy.

I hope this explanation provides some useful insight into the current behavior. In the meantime, you may also consider starting a new discussion in the Tech Community, where other administrators can share feedback and practical suggestions based on their real production environments and experience.

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