Windows Authentication is not working for internal OWA

Hi,

I have two Exchange 2010 Servers.

When I try to open OWA internal with https://exchange01.domain.local/owa

I get prompted for user + password although I have configured owa authentication on the servers with:

X Use one ore more std. auth. methods:

X Integrated Windows authentication

I restartet iis and the servers as well but no changes.

How can I get rid of the prompt and automatically get logged in?

(Users and Exchange are in the same domain.local Domain, no certificate issues because
I used our CA RootCert for issuing certs for the exchange servers and the Root CA is trusted
by all clients,servers)

Thanks!