How to configure UTM 9.4 with Exchange 2010 OWA with reverse authentication

Hi all

i'm trying to have OWA from Exchange 2010 working with reverse authentication over a Sophos 9.4 but not able to have it working. Does anybody have any expirience with how to configure the UTM? Do i need to configure Exchange OWA just with Basic Authentication? I tried to configure the system with this guide:

https://sophserv.sophos.com/repo_kb/120454/file/Exchange%20WAF%20Guide%20-%20UTM%209.3%20-%20Nov%202015.pdf

I receive a Pop-Up where i can enter the credentials but i can't login with it.

Many thanks for your help.

 

Best regards,

Marc