In our organization we deploy zimbra server having Release 7.2.0_GA_2669.RHEL6_64_20120410002025 CentOS6_64 FOSS edition version. I want to secure port 25 by using smtp-auth or any technique but not by using "mynetwork" so who can send mail from unwanted telneting to zimbra server's port 25 through command prompt. I want that if any one try to send mail from command prompt is shold be asked for Authentication. My zimbra server is using Active Directory for authentication. So help me how to get this?