In the default exchange 2003 FE/BE configuration, kerberos is used for authentication. we have our FE in DMZ. we opened UDP/TCP 88 to our domain controllers. we are seeing some warnings on FE: Microsoft Exchange Server has detected that NTLM-based authentication is presently being used between this server and server 'BE'. NTLM is still a secure authentication mechanism and protects users' credentials. However, this indicates that there may be a configuration issue preventing the use of Kerberos authentication. If this condition persists, please verify that server 'BE' is properly configured to use Kerberos authentication. After applying any changes it may be necessary to restart Internet Information Services on both the front-end and back-end servers. my question is: Do we need to open port 88 UDP/TCP from DMZ to Back End server also? I would greatly appreciate any help, thanks,