We want to change from F5 LB to HAProxy and pretty much all services are switched already. As long as we have Exchange 2016 behind the F5 everything works just fine. As soon as we switch it over to HAProxy we experience "401 Unauthorized" errors and Outlook is permanently asking for credentials without getting a connection. The MS Connection test is giving us a hint to autodiscover.xml.
We tried to use a curl command to send the post to Exchange/autodiscover/autodiscover.xml and we get a proper authorization here and the corresponding XML. What does Outlook do different from what a curl command does?