Kerio and Active Directory authentication not working

Authentication problems with Kerio Mail Server. When on the “Diagnostic” tab under accounts > diagnostics. There it says username@domain.com@mail.domain.com:993. I can’t authenticate and that authentication string seems weird. We have Kerio with AD integration. Why can’t a client authenticate?

IMAP doesn’t seem to authenticate either which is also weird, similar problem I suspect that it isn’t authenticating the user account properly.

Login conventions I tried:
user@domain.com
user
domain\user

Filip Navara wrote:
The Kerio server sometimes reports that NTLM authentication is supported even though the NTLM authentication is supported only for certain users on the server. The problem is that the server doesn’t actually tell the client why the authentication failed and it’s not apparent in the server logs either. Try disabling the NTLM authentication on the server and see if it helps.

https://discourse.emclient.com/emclient/to…