You have multiple Active Directory sites in a Microsoft Exchange Server 2013 environment.
You configure Outlook Web App virtual directories on all Client Access servers in each site with the same Internal URL and External URL, such as mail.xxxxxxx.com.
Notexxxxxxx is the name of the domain.
A Client Access server handles a proxy request for a cross-site user who uses a different URL to sign into Outlook Web App. For example, the user tries to sign into Outlook Web App through owa.xxxxxxx.com.
In this scenario, the Client Access server redirects the user to the External URL of the Client Access server on which the user is located, and the user sees the following message:
Use the following link to open your mailbox with best performance
The expected behavior is that the Client Access server should be a proxy for the user to the Mailbox server on which the user is located.
This issue occurs because of a logic defect in the Outlook Web App proxy and redirection.
To resolve this issue, install the following service pack:
2926248 Description of Exchange Server 2013 Service Pack 1
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about the Exchange Server 2013 Client Access role, go to the following Microsoft website: