The page should display a series of XML commands which are used to download and install the add-in into your environment.
If you are using a proxy server, make sure to test access to the site via direct as well as via the proxy.
Ensure that the administrator has the correct Exchange roles assigned to install the add-in. Refer to the Microsoft TechNet article for general information on required administrator permissions and instructions for installing an Outlook Add-in.
If you are using Exchange server 2013, please ensure cumulative update 11 has been installed. For more information refer to this Microsoft article.
If the URL is not available, contact our Symantec technical support via phone or by opening a support case with this information for analysis.