Good evening, with the help of a debugging proxy I found the reason for the certificate warning in Outlook and I think it is a bug of XG´s web filtering module. Let us assume the connection to Outlook Anywhere goes via mail.company.com. During autodiscover, Outlook automatically tries to establish a connection to the main domain company.com. However, company.com exists in DNS, but the server does not accept HTTPS connections. If I open that URL without XG web filtering in my browser, I get a "page cannot be displayed" error. After activating web filtering (without HTTPS scanning, of course), I get a certificate warning. If I ignore this and continue, I get a blank page. The CA of the certificate shown is from my Sophos XG. This is also the solution for the question why I could connect to another Exchange 2013 system without certificate warning. For this server, the URL https://company.com is available and thus there is no interference with the Sophos CA. Kind regards, Matthias
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